NEW YORK?An explosion rocked a 10-story commercial building Thursday, spraying glass and rubble across a quiet block and injuring up to 50 people, authorities said.

Several victims, at least three in serious condition, were taken to four Manhattan hospitals for treatment. St. Vincent’s hospital said it was treating eight patients.

A preliminary injury total stood at 50, said police spokesman Michael O’Looney. A tally of hospitals showed at least 20 people were taken to four of them; other people were treated at the scene.

Windows along the block were blown out by the force of the blast, and several of the injured were hit by flying glass.

Plumbers were working on the boiler in the commercial building at the time of the 11:30 a.m. blast, but it was unclear if that was the cause of the explosion.

Law enforcement officials said it did not appear to be an act of terrorism.