The explosion at New York City's Port Authority subway terminal was an attempted terrorist attack, authorities have confirmed.

Mayor Bill de Blasio confirmed that the explosion was a planned attack, but said there were no other credible threats to the city at this time.

Four people, including the suspect, were injured in the rush-hour blast in one of New York's major transit centres, authorities said. Three commuters suffered minor injuries, while the alleged attacker's injuries were more severe.

The alleged attacker has been identified as 27-year-old Akayed Ullah, Police Commissioner James O'Neill said. Multiple outlets reported that Mr Ullah was a Bangladeshi native who had been living in the US for the last seven years, citing police sources.

Asked if Mr Ullah had ties to Isis, Mr O'Neill said the alleged attacker had made statements, but declined to elaborate as to what they were. Mr O'Neill said the suspect had been transported to Bellevue Hospital with burns and other wounds.

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Mr Ullah allegedly detonated an "improvised, low-tech explosive device" that was strapped to his body with velcro and zip ties, Mr O'Neill said. Police responded to the explosion caused by the device at approximately 7:20 am ET. The terminal resumed service three hours later.

The device went off in an underground walkway connecting trains at 42nd St and 8th Avenue. The area is a popular hub for commuters, as well as tourists. Seasonal attractions such as the Rockefeller Christmas tree and festive store displays draw visitors to the area in the winter months.

The incident was captured on transit system video, Mr O'Neill said. Authorities were deployed to other transportation hubs in the city as a precautionary measure.

Explosion on New York City subway injures four

Governor Andrew Cuomo urged New Yorkers to return to work, saying: “We’re not going to allow them to disrupt us. That is exactly what they want, and that is exactly what they’re not going to get."

"This is New York and we all pitch together, and we are a savvy people, and we keep our eyes open," he added. "...We have the best law enforcement on he globe, and we’re all working together extraordinarily well."

The attack occurred less than two months after a man drove a rental truck through a New York City bike path, killing eight. He claimed to have carried out the attack in the name of Isis.