Police and firefighters are on the scene of a possible explosion in New York City.

According to the Fire Department, the blast occurred shortly before 9pm local time on West 23rd Street at 6th Avenue in the Chelsea section of Manhattan.

There are multiple reports of 25 people injured, but none thought to be life-threatening.

The FBI and NYPD Counterterrorism Unit are investigating but there is no confirmation on what caused the blast yet.

First responders fear there could be a secondary device, though none have been found yet.

Authorities have ruled out gas as a cause of the explosion.

All this comes hours after a pipe bomb exploded in Seaside Park, New Jersey, shortly before thousands of runners participated in a charity 5K race to benefit Marines and sailors.