In what New York City Mayor  Bill de Blasio  called a "cowardly act of terror," a man driving a rental truck struck and killed eight people on a bike path Tuesday afternoon.

The sprawling  crime  scene runs about 10 blocks along the West Side Highway, a few blocks away from  One World Trade Center.

Witness Andrew Howell said he was walking along the path when he saw a truck plow into two cyclists riding about 20 feet in front of him; he said the impact sent one of the victims straight up into the air, and the man was motionless when he landed back on the ground. The driver then continued at a high speed before crashing, Howell said.

A uniformed police officer was credited with stopping the carnage.

A suspect is in custody and was identified as 29-year-old Sayfullo Saipov of Tampa, Florida, multiple law enforcement officials told ABC News.

The suspect is reported to have screamed "Allahu Akbar" after the crash, and that is a key reason authorities are looking at  terrorism  as a possible motive, sources said.

Saipov left a note saying he carried out the attack on behalf of ISIS, law enforcement officials tell ABC News.

The NYPD and FBI are "seeking the public’s assistance in the investigation into the terrorist act that occurred in lower Manhattan earlier today. The public is urged to share any images or videos that could assist in the investigation," according to a statement from the NYPD.

New York Gov.  Andrew Cuomo  said there was no evidence of a wider, ongoing threat but he said more police would be monitoring the streets on Halloween night. The city's annual Halloween parade in the West Village will still take place tonight, officials said.

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The deadly incident began at about 3:05 p.m., when the vehicle -- a Home Depot rental truck, according to the company -- entered the West Street pedestrian and bike path north of Chambers Street, hitting multiple people on the path, New York City police said.