City firefighters say an overloaded extension cord is to blame for a two-alarm fire in Upper Manhattan Tuesday morning that left at least 12 people hurt.

“There were multiple people trapped above the fire here in extreme conditions of heat and smoke,” said FDNY Commissioner Daniel Nigro.

The FDNY said flames broke out around 4:30 a.m. on the fifth floor of a six-story building located at 545 West 158th Street in Washington Heights.

Fire officials said that the first FDNY crews arrived at the scene just four minutes after the initial 911 call.

One person suffered serious injuries. All the others are said to have sustained non-life threatening injuries.

Members of Ladder 23, Ladder 34 and Squad 41 were among the crews who arrived on scene to rescue residents. Firefighter Abraham Miller of Ladder 23 was among the rescuers who tried to save residents from the roof. 

“When we were up there. all we heard was screams, like a lot of people screaming, little girl screaming, adults screaming, and we were trying to figure out where those screams were coming from,” said Miller.

Miller said that he and another firefighter conducted a rope rescue from the roof in order to help a child and a woman below them. 

“When we looked over the side of the building, we saw a little girl's hands on the window guards. Her grandmother was holding her up trying to get her just so she could breathe,” Miller said. 

Fire officials said that rope rescues are rare but pointed out that having two happen simultaneously, as they did in this case, was very unusual. Even so, firefighters across the city train for rope rescues once a week.