NEW YORK — A 29-year-old man driving a rental truck plowed down people on a Manhattan bike path Tuesday in what authorities described as a terrorist attack that killed eight and injured 11 before the suspect was shot and arrested by police.

A sunny fall day along the Hudson River erupted in chaos just around the time students were getting out from nearby Stuyvesant High School, when a rented Home Depot truck turned on to the bike path along the West Side Highway.

Witnesses say the speeding truck struck unsuspecting bicyclists and pedestrians while onlookers screamed and scattered. The truck then veered left toward Chambers Street, where it collided with a small school bus, injuring two adults and two children inside, officials said.

Foreign ministries of Belgium and Argentina said five Argentines and a Belgian were among the victims. The Argentine nationals were part of a group of friends celebrating the 30th anniversary of their high school graduation, the Argentine Foreign Ministry said in a statement Tuesday.

According to a video from the scene, the man then jumped out of the wrecked vehicle brandishing what appeared to be handguns. Some witnesses said he shouted “Allahu akbar’’ meaning “God is great’’ in Arabic.

The attack could intensify the political debate over immigration and security. President Trump has argued for much tougher screening of immigrants to prevent terrorism, and opponents of those policies have sought to block his efforts in the courts. Uzbekistan was not among the countries named in any version of the president’s travel ban, which largely targeted a number of majority-Muslim countries.

[ New York vehicle attack: Everything you need to know ]

Trump responded to the attack on Twitter, saying it “looks like another attack by a very sick and deranged person.’’ He tweeted a short time later: “We must not allow ISIS to return, or enter, our country after defeating them in the Middle East and elsewhere. Enough!” ISIS is an acronym for the Islamic State.

On Tuesday night Trump said he was tightening immigrant screening, tweeting: “I have just ordered Homeland Security to step up our already Extreme Vetting Program. Being politically correct is fine, but not for this!”

I have just ordered Homeland Security to step up our already Extreme Vetting Program. Being politically correct is fine, but not for this!

— Donald J. Trump (@realDonaldTrump) November 1, 2017

There was no immediate indication that the attack had been directed by the Islamic State. However, the group has called on its supporters in Western countries to launch their own attacks, using anything at hand as weapons, including vehicles.

Inside the rental truck, investigators found a handwritten note in which Saipov had declared his allegiance to the Islamic State, according to officials.

Saipov is expected to survive, meaning investigators will likely have a chance to question him about his motive for the attack, but so far, they said, he appears to have been a “lone wolf’’ suspect – someone who acted alone after being inspired, but not directly instructed, by the Islamic State.

He had been living in Paterson, New Jersey before the attack, and rented the vehicle in that state before driving it into Manhattan, officials said.

The violence was terrifyingly similar to vehicle attacks carried out in Europe, where Islamic State supporters have used cars and trucks to strike pedestrians in crowded streets, a tactic that has been employed in France, Britain, Germany, Sweden and Spain.

“This certainly bears all the hallmarks of an ISIS-inspired or al-Qaeda-inspired attack,” said Rep. Adam B. Schiff (Calif.), the ranking Democrat on the House Intelligence Committee, whom the FBI briefed on the attack Tuesday evening. “We have to expect that as the capital of the caliphate has now fallen, there are going to be increasing efforts to show that they remain dangerous and lethal, and to expand the virtual caliphate.”

Antonio Valasquez, 28, said he saw the truck speed by as he left a restaurant and then heard a crash. “I didn’t really understand, you know, at first what was happening,” he said. Valasquez said he heard what appeared to be gunshots shortly after but couldn’t be sure. “I was running away.”

An officer from the 1st Precinct approached Saipov and shot him in the abdomen, police said. He has been taken to a hospital, but officials did not discuss his condition or location. The weapons he was brandishing turned out to be a pellet gun and a paintball gun, police said.

Rabbi Chaim Zaklos was picking up about half a dozen children from school to escort them to Hebrew school nearby when he encountered the scene. Police were pushing people away, and he could see abandoned bikes and what appeared to be uprooted trees nearby. “It was obvious something drastic was happening, so I just wanted to get the kids someplace safe,” said Zaklos, 35.

“This is a very painful day in our city,’’ New York City Mayor Bill de Blasio (D) said. “Based on the information we have at this moment, this was an act of terror, a particularly cowardly act of terror aimed at innocent civilians.”

Saipov moved to the United States from Uzbekistan about six years ago, said Dilnoza Abdusamatova, 24, who said Saipov stayed with her family in Cincinnati for his first two weeks in the country because their fathers were friends. Some officials said he arrived in 2010.

Abdusamatova said Saipov then moved to Florida to start a trucking company. Her family members think he got married about a year after arriving in the United States and may now have two children. Around that time, she said, he cut off contact with them.

“He stopped talking to us when he got married,” Abdusamatova said.

[ Vehicles as weapons of terror: U.S. cities on alert as attacks hit the West ]

Saipov had lived in an apartment complex, Heritage at Tampa, near the Hillsborough River. On Tuesday evening, two plainclothes investigators were seen departing the community, having interviewed several residents and others in the surrounding neighborhood. The investigators declined to answer any questions.

“Four FBI agents came and told me he used to live here,” said Venessa Jones, who said she lives in an apartment above the one Saipov rented. Neighbors at the complex said they didn’t know Saipov.

Officials said they had no information to suggest that the attacker had any accomplices or that there was a further threat to the city.

Nevertheless, they said, extra police would be posted around the city as a precaution, particularly along the route of the Halloween Parade, a long-standing tradition in Manhattan’s Greenwich Village that attracts big crowds. Officials said sand trucks, police vehicles and other equipment would be used to deter any vehicle attacks at the parade.

Rosario’s local newspaper, La Capital, described the vacation to New York as the “trip of their dreams,” and reported that they were riding bicycles in Lower Manhattan before the attack.

The local newspaper’s headline read:  “A trip of camaraderie among friends from Rosario turns into tragedy.”

Barrett, Lowery, Siegel, and Schmidt reported from Washington. Philip Bump in New York, Jon Silman in Tampa, and Julie Tate, Ellen Nakashima, Jennifer Jenkins, Mark Berman in Washington contributed to this report.

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Newly released court documents show that Trump foreign policy adviser George Papadopoulos communicated with several senior campaign officials about his outreach to the Russian government over a period of months. The recipients of Papadopoulos’s emails are not named in the filings, but The Washington Post has identified several individuals based on interviews and other documents. Papadopoulos pleaded guilty this month to lying to federal agents about his outreach to Russia.

“The Campaign Supervisor”: Trump campaign national co-chairman Sam Clovis

Victoria Toensing, an attorney for Sam Clovis, confirmed that several references in court filings to “the campaign supervisor” refer to the onetime radio host from Iowa, who served as Trump’s national campaign co-chairman.

At one point, Papadopoulos emailed Clovis and other campaign officials about a March 24, 2016, meeting he had in London with a professor, who had introduced him to the Russian ambassador and a Russian woman he described as “Putin’s niece.” The group had talked about arranging a meeting “between us and the Russian leadership to discuss U.S.-Russia ties under President Trump,” Papadopoulos wrote. (Papadopoulos later learned that the woman was not Putin’s niece, and while he expected to meet the ambassador, he never did, according to filings.)

Clovis responded that he would “work it through the campaign,” adding, “great work,” according to court documents.

In August 2016, Clovis responded to efforts by Papadopoulos to organize an “off the record” meeting with Russian officials. “I would encourage you” and another foreign policy adviser to the campaign to “make the trip, if it is feasible,” Clovis wrote.

Toensing said Clovis “always vigorously opposed any Russian trip for Donald Trump and/or the campaign.” She said his responses to Papadopoulos were courtesy by “a polite gentleman from Iowa.”

“High-Ranking Campaign Official”: Campaign manager Corey Lewandowski

Emails previously described to The Post indicate that the “high-ranking campaign official” described in court documents is onetime campaign manager Corey Lewandowski. The emails were among more than 20,000 pages that the Trump campaign turned over to congressional committees after review by White House and defense lawyers.

Lewandowski, who was pushed out of his post in June 2016, did not respond to requests for comment.

Papadopoulos wrote to Lewandowski several times to let him know that the Russians were interested in forging a relationship with the campaign, court filings show.

In one email on April 27, 2016, Papadopoulos wrote “to discuss Russia’s interest in hosting Mr. Trump.”

“Have been receiving a lot of calls over the last month about Putin wanting to host him and the team when the time is right,” he added.

In May, Papadopoulos forwarded to Lewandowski an offer of “cooperation” from a Russian with links to the Ministry of Foreign Affairs. “Is this something we want to move forward with?” he asked.

There is no indication if or how Lewandowski responded to those messages. But in June, when Papadopoulos emailed him again about Russia, Lewandowski referred him to Clovis because he “is running point,” according to court documents.

[Top campaign officials knew of Trump adviser’s outreach to Russia]

“Another high-ranking campaign official”: Campaign chairman Paul Manafort

The court filings indicate that Papadopoulos emailed “another high-ranking campaign official” on May 21, 2016, with the subject line “Request from Russia to meet Mr. Trump.”

The Post has previously identified this official as Paul Manafort, who was indicted Monday on unrelated criminal charges.

Manafort forwarded Papadopoulos’s email to another campaign official, stating: “We need someone to communicate that DT is not doing these trips,” referring to a trip to Russia. “It should be someone low level in the campaign so as not to send any signal.”

Manafort spokesman Jason Maloni in August told The Post that the campaign chairman’s response indicated that “any invitation by Russia, directly or indirectly, would be rejected outright.”

“Another campaign official”: Manafort deputy Rick Gates

The Post has previously identified the official who received the May 21, 2016, email from Manafort as his deputy, Rick Gates. Gates was indicted Monday on unrelated criminal charges.

“Senior Policy Advisor”: Unknown

The court filings indicate that on April 27, 2016, Papadopoulos emailed a “senior policy advisor” and wrote, “Have some interesting messages coming in from Moscow about a trip when the time is right.”

The Post has not identified this official.

“The Professor”: Joseph Mifsud, director of the London Academy of Diplomacy

According to emails previously described to The Post, the London-based professor who was a key contact for Papadopoulos in his Russian outreach is Joseph Mifsud, who formerly served as a government official in Malta.

Mifsud did not respond to a request for comment Monday. In an email to The Post in August, he wrote that he had “absolutely no contact with the Russian government” and said his only ties to Russia were through academic links.

Papadopoulos met Mifsud in March 2016 while traveling in Italy, according to court records. The professor “seemed uninterested” in Papadopoulos until he learned that he was a campaign adviser, according to court filings.

Five days after Trump named Papadopoulos as one of his advisers during a meeting at The Post, Papadopoulos and Mifsud met in London. The professor brought with him a Russian woman who was introduced as a relative of President Vladi­mir Putin who had connections to senior Russian government officials.

The following month, Mifsud told Papadopoulos that he had just returned from Moscow, where he had learned from high-level Russian government officials that Russia had “dirt” on Democratic presidential candidate Hillary Clinton, including “thousands of emails.”

“The Female Russian National”: Unknown

Court documents show that Papadopoulos corresponded with a “female Russian national” whom he initially believed was Putin’s niece.

At one point, she wrote to him, “The Russian Federation would love to welcome [Trump] once his candidature would be officially announced.”

The Post has not identified the woman.

“A Russian National Connected to the Russian Ministry of Foreign Affairs”: Ivan Timofeev

In April 2016, Mifsud introduced Papadopoulos over email to a man in Moscow who told Papadopoulos that he had connections to the Russian Ministry of Foreign Affairs, court records show.

Emails previously described to The Post indicate that the man is Ivan Timofeev, a program director at a Russian government-funded think tank called the Russian International Affairs Council.

Papadopoulos communicated via Skype and email with Timofeev to discuss establishing ties between Russian officials and the Trump campaign.

On Monday, Timofeev declined to comment, referring a reporter to a statement the Russian International Affairs Council posted in August in response to a Post story. The statement said that Papadapoulos had contacted the council and “put forth the idea of a possible visit to Russia by Mr. Trump or his team members.”

“Given the RIAC’s established practice of hosting public meetings with prominent politicians and public figures from the U.S. and other countries, the U.S. initiative was a matter of routine for the Council,” the statement said, pointing out that among the council’s guest speakers was former U.S. ambassador Michael McFaul.

Timofeev told The Post in August that the idea of a meeting with Trump officials was dropped after he received no official request from the Trump campaign for a meeting.

David Filipov in Moscow, Karla Adam in London, and Tom Hamburger and Robert Costa in Washington contributed to this report.