A two-alarm fire on Manhattan’s Upper East Side left 19 people injured early Saturday morning after the building’s alarms failed to go off, authorities said.

The fire began around 3:45 a.m. on the 12th floor of a high-rise building on Second Avenue and 92nd Street and was contained to one apartment, fire officials said.

The building’s centralized alarm system did not detect the fire and a security guard in the building’s lobby had to be alerted about the fire by a passerby, authorities said

It took over 100 firefighters more than two hours to get the fire under control. While the flames were contained to one apartment, smoke quickly traveled through the hallways and vents of the 40-story tower.

The cause of the fire remains unknown. An investigation is ongoing.

(Source: NBC New York)