NEW YORK (CBSNewYork) -- Three people were hurt when a fire broke out overnight on the Upper East Side.

It happened just before 1:30 a.m. Tuesday on 78th Street near Second Avenue.

The FDNY said the fire started on the third floor of a six story building.

One person suffered life-threatening injuries. Another suffered serious but non-life-threatening injuries, and a third had minor injuries.

The cause of the fire is under investigation.