A fire began early Tuesday near Penn station in New York and blazed for hours before it was finally brought under control by firefighters. More than hundred firefighters were present at the location to douse the fire, which led to train delays.

The New York City fire department said that the fire was a three-alarm blaze and the subway trains A and E were told not to stop at the Penn station because of the fire. It is not clear what caused the blaze, but reports said that the fire began after 2:30 a.m., local time, at construction sheds two floors below Eighth Avenue and West 33rd street, according to WABC-TV New York. Penn station was reportedly kept open despite the fire.

Subway service returned to normal by 5:30 a.m. with residual delays.

Firefighters had also reportedly cut power to some Long Island Rail Road tracks, but the move did not affect service immediately. However, service may be affected later in the day, WABC-TV New York reported.

It was not clear how the fire, which is being called “suspicious” by officials, started but two firefighters suffered minor injuries fighting the flames, NBC News reported. All lanes on 33rd Street between 7th and 9th Avenues, and on 8th Avenue between 28th to 36th Streets were closed. Two lanes were also blocked on the 34th Street between 7th and 8th Avenues. 

Earlier on Monday, a tunnel filled with smoke forced the evacuation of a Washington Metro station, leaving one person dead and sending 84 people to the hospital. The cause of the smoke was, however, not immediately determined.