The 29-year-old driver, named by police as 29-year-old Sayfullo Saipov was shot in the abdomen by police and taken into custody after jumping out of the truck with what turned out to be a fake gun in each hand and shouting "Allahu Akbar" officials said.
The man underwent surgery and was in critical condition but was expected to survive.
He has a Florida driver's license but may have been staying in New Jersey, they said. The witness, who was identified only as Eugene, said bodies were lying outside Stuyvesant High School, one of the city's elite public schools.
Earlier, reports came out that police are responding to reports of gunfire.
The Islamic State has been encouraging its followers to mow down people, and England, France and Germany have all seen deadly vehicle attacks in recent months and years.
"I saw the gun running in a circle and I realised it was serious", he said.
A police officer was apparently shot and suffered a minor injury.
The New York Police Department posted on its Twitter feed that one person was in custody.
Cities around the globe have been on alert against attacks by extremists in vehicles. The two-lane path is separated by a low median from West Street, part of the West Side Highway.
At least six people are dead and 15 others are injured on the West Side of Manhattan after a white rental truck drove on to a bike path Tuesday afternoon, moving south on West Street near Chambers Street in Manhattan at around 3:10 pm in the TriBeCa neighborhood.
"People were screaming. Females were screaming at the top of their lungs".
New York Mayor Bill de Blasio said he had been briefed about the incident and that "there is no active threat now".
Multiple reports said the truck struck at least five people.
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