A man with a pipe bomb strapped to his body with Velcro and cable ties set off the crude device in the subway near Times Square on Monday, injuring himself and three other people at the height of the morning rush hour.
All four were being treated for non-life-threatening injuries in what the mayor and police labelled an attempted terror attack.
The explosion happened in a long underground passageway that runs a full city block under 42nd Street between Seventh and Eighth Avenues.
The 7.20am blast caused smoke to fill the passageway, which was crowded with Monday morning commuters.
Mayor Bill de Blasio and police commissioner James P. O’Neill labelled it an attempted terror attack.
“Thank God the perpetrator did not achieve his ultimate goals,” Mr de Blasio said.
The suspect was identified as 27-year-old Akayed Ullah.
Law enforcement officials said he was inspired by the Islamic State group but had apparently not had any direct contact with the group.
(PA Graphics)
He lives in Brooklyn and may be of Bangladeshi descent, it was thought.
Authorities said the bomb was a low-tech explosive device.
They were investigating how it was made, and combing through surveillance footage that captured the blast on video.
A video posted on social media showed the security footage.
In it, a man walks through the crowded pedestrian tunnel and the bomb suddenly going off in a plume of white smoke.
Through the smoke, the suspect is then seen sprawled on the ground as bystanders flee.
Fire officials said the suspect had burns to his hands and abdomen.
The others who were injured suffered ringing in ears and headaches.
Police are investigating whether Ullah intended to set off the device in the walkway, or whether he had meant to do it in a busier location.
A photo published by the New York Post showed a bearded man crumpled on the ground with his shirt apparently blown off and black soot covering his bare midriff.
A police officer is holding the man’s hands behind his back.
The explosion triggered a massive response by police and firefighters both above and below ground, tangling subway and bus service at the nearby Port Authority bus terminal.
Elrana Peralta, a customer service worker for Greyhound, said she works in the Port Authority terminal complex near where the blast happened, but did not hear the explosion.
Police block a street by Port Authority Bus Terminal (Andres Kudacki/AP)
“All we could hear was the chaos,” she said. “We could hear people yelling, ‘Get out! Get out! Get out!'”
New York has seen its share of terror attacks in recent years.
On October 31, a man drove a rented truck onto a bike path near the World Trade Centre, killing eight people.
Video from above the “Crossroads of the World” showed lines of police and emergency vehicles, their lights flashing, lining the streets and no other vehicle traffic moving.
Everything around the Port Authority area was shut down for a few hours, a surreal scene of still at what would ordinarily be a bustling rush hour. But by 10am, much of the area had returned to normal.
Authorities said by evening rush hour everything would be re-opened.
White House Press Secretary Sarah Sanders tweeted that President Donald Trump had been briefed on the explosion.