An Uzbek immigrant accused of killing eight people in New York City by driving a rental truck down a riverfront bike path on Tuesday appeared to have acted alone, but the Hallowe'en Day attack had all the hallmarks of terrorism, authorities said.

The suspect, who was shot by police and arrested moments after Tuesday's rampage on the Lower West Side of Manhattan, left a note saying he carried out the attack in the name of the militant Islamic State group, the New York Times and CNN said.

Christian leaders responded with prayer and calls for unity, and warnings about the spread of Islamist ideology. 

The death toll paled in comparison to dozens killed in similar assaults last year in France and Germany. However, it was still the bloodiest single attack on New Yorkers since September 11, 2001, when suicide hijackers crashed two jetliners into the World Trade Center, killing more than 2,600 people.

The Twin Towers site was just a few blocks from the scene of the carnage left when the suspect swerved the pickup onto a path filled with pedestrians and bicyclists on a sunny, crisp autumn afternoon.

Driving at speeds estimated at more than 60 mph, the vehicle mowed down everyone in its path before slamming into the side of a school bus.

The man then climbed out of the vehicle brandishing what appeared to be a pair of handguns before he was confronted by a city police officer, who shot him in the abdomen. Police said they recovered a paint-ball gun and a pellet gun from the scene.

The attack was over in a matter of seconds. Video footage taken by a bystander that circulated online showed crumpled bicycles scattered long the path, and at least two people lying on the ground.

In addition to the eight fatalities, at least 11 people were hospitalised for injuries described by fire officials as serious but not life-threatening. That excluded the suspect, who underwent surgery for gunshot wounds.

Police declined publicly to identify the man, but a source familiar with the investigation said his name was Sayfullo Saipov, 29. He reportedly lived in Paterson, New Jersey, a one-time industrial hub about 25 miles (40 km) northwest of lower Manhattan.

He had rented the pick-up from a Home Depot hardware store which, according to media accounts, was located in Passaic, just south of Paterson.

Six victims were pronounced dead at the scene and two more at a nearby hospital, Police Commissioner James O'Neill said.

Five of the dead were Argentine citizens, visiting New York as part of a group of friends celebrating the 30th anniversary of their high school graduation, the Argentina Foreign Ministry said in a statement. Belgium's foreign minister said a Belgian citizen was also among those killed.

A US law enforcement official described the suspect as a US immigrant born in Uzbekistan, a predominantly Muslim country in central Asia that was once part of the former Soviet Union. CNN and NBC News reported that he entered the United States in 2010.

Authorities late on Tuesday surrounded a house in Paterson where, according to the New York Times, Saipov was believed to have lived. Paterson, known for its large immigrant population, is home to about 150,000 people, including 25,000 to 30,000 Muslims.

ABC News reported that Saipov had lived in Tampa, Florida. A check of court records related to a traffic citation that Saipov received in eastern Pennsylvania in 2015 showed he listed addresses then in Paterson and Cuyahoga Falls, Ohio.

Although authorities from the mayor's office to the US Department of Homeland Security all swiftly branded the attack an act of terrorism, Governor Andrew Cuomo stressed that the suspect was believed to have acted alone.

'There's no evidence to suggest a wider plot or a wider scheme. These are the actions of one individual meant to cause pain and harm and probably death,' Cuomo told a news conference two hours after the rampage.

Asked later in a CNN interview whether the suspect had been known to authorities before the attack, Cuomo replied: 'It's too early to give you a definitive answer.'

The New York Times said investigators quickly recognised that Saipov had come to the attention of law enforcement in the past.

It cited three officials as saying federal authorities knew of Saipov from an unrelated probe, although it was unclear whether that was because he had ties to someone who was under scrutiny or because he was the target of an investigation.

CNN and other media outlets, citing police officials, reported that the suspect shouted 'Allahu Akbar' – Arabic for 'God is greatest' – when he jumped out of his truck.

O'Neill said only that an unspecified comment by the suspect when he exited his truck, and the general circumstances of the assault, led investigators to label the incident a 'terrorist event'.

The Federal Bureau of Investigation joined the New York City Police Department and other agencies in a Joint Terrorism Task Force to conduct a probe of the attack, the FBI said in a statement.

Despite the attack, thousands of costumed Halloween revellers turned out hours later for New York City's main Halloween parade, which went on as scheduled on Tuesday night with a heightened police presence just a few blocks away.

US President Donald Trump, who has pressed for a ban on travellers entering the United States from some predominantly Muslim countries, said on Twitter that he had ordered Homeland Security officials to 'step up our already Extreme Vetting Program. Being politically correct is fine, but not for this!'

Evangelical supporters of the US president expressed their support, with Robert Jeffress, pastor of First Baptist Church, Dallas, linking the event with dramatic developments yesterday in the investigation into collusion between the Trump campaign and Russia. He tweeted: 'Unless Mueller has pic of @POTUS holding flashlight for Russians brking in voting machines, don't care abt Russia. This is why I support DJT.'

Broadcaster and conservative activist Dr James Dobson said: 'Every new act of terror that targets innocent lives is a tragic and terrible reminder of the evil that exists in our world. This particular attack is perhaps made even more painful by its proximity to the World Trade Center. Make no mistake, this is pure cowardice veiled in violence. True bravery belongs to the first responders and specifically the police officer credited with helping end this violence before even more were injured or killed.

'We pray for the people of New York, many of whom are likely reliving the pain of 9/11 all over again. We pray also for the families who have lost loved ones on what should have been a normal fall day like any other. Finally we pray for the end of the hateful ideology that gives birth to these senseless and barbaric acts.'

Cardinal Daniel DiNardo, president of the US Conference of Catholic Bishops, said: 'To you and to everyone, I would like to say that the forces of darkness always try to wipe away our hope, but our hope is in the name of the Lord and will always remain firm. Let us remember the words of the Lord to prophet Joshua: Be strong and steadfast! Do not fear nor be dismayed, for the Lord, your God, is with you wherever you go.'

Cardinal Timothy Dolan, the Catholic Archbishop of New York, said: 'Today our city and our nation are stunned and horrified by another act of senseless violence.

'While details continue to emerge, one thing is clear: once again, no matter our religion, racial or ethnic background, or political beliefs, we must put our differences aside and come together in faith and love to support those who are injured, pray for those who have died as well as their families and loved ones, and work towards greater respect and understanding among all people so that heinous and evil acts like this become a thing of the past.'

Additional reporting by Reuters.