A three-alarm fire on New York City’s Upper East Side sent plumes of black smoke into the sky on Friday as people in the neighborhood reported hearing an explosion.

It happened at a six-story apartment building at 305 E. 95th St., between Second and First Avenues, in Manhattan.

The FDNY said they were called to the building just after 10 a.m. for a report of a fire on the roof. It quickly escalated to a three-alarm fire with over 40 units and 170 members, including EMS workers, officials said.

Videos showed the bright orange flames and thick, black smoke shooting from the roof and into the sky above. More videos showed firefighters on the roof as the flames billowed out of the structure.

The fire spread to the building’s cockloft and three penthouses before it was contained, FDNY Deputy Assistant Chief James Canty said.

The NYC Office of Emergency Management advised people nearby to close their windows because of the smoke and said to expect traffic delays in the area.

According to the City Department of Buildings, there was a partial stop-work order from 2015 for a cellar apartment that was illegally constructed. It’s unclear if it’s connected to the fire.

Canty said the cause of the fire is under investigation and that three firefighters suffered minor injuries.