NEW YORK - The city fire department is investigating the cause of an early morning fire Thursday on the Upper East Side that left one person dead and more than a dozen others injured.

The FDNY says the six-alarm fire broke out around 3:30 a.m. at an apartment building located at 324 East 93rd Street in Yorkville.

Firefighters found one man dead on the third floor.

26-year-old Jessica DeMorris and 24-year-old Rocco Clauss were sleeping when they say a fire broke out in the living room of the ground-floor apartment where they have been staying.

"I ran through the living room with both dogs in my arms completely engulfed by flames," Clauss said.

The fire destroyed the five-story building. Clauss and DeMorris say they had been housesitting and dog sitting for friends.

"The people whose apartment it is is in Mexico and they are going to have to come home to this tonight," DeMorris said.

The fire commissioner said the fire spread quickly, in part because the couple left the door open when they fled.

The blaze drew 250 firefighters and emergency workers from 50 units across the city.

Dozens of people were forced into the street, some wearing only their pajamas, as several other buildings were evacuated.

Most of those living in the adjoining buildings were able to return to their homes.

"The building is totally destroyed, but we were able to save the buildings that are attached on either side," FDNY Chief of Department James Leonard said.

Three firefighters also rescued a man who was yelling for help from a top story window. They used a rope to lower him and a firefighter to the ground. Once they got to the ground, that rope burned away.

“The gentleman on the fifth floor was trapped with fire coming up the stairs and fire blocking the fire escape, and his two options were really to jump or to burn, and a firefighter was lowered from the roof  in very dangerous fire and heat conditions," Fire Commissioner Daniel Nigro said. "That was the only way in which this man could have been saved.”

"I just told him to stay calm and when we got down I said I hope you enjoyed the ride. He sort of smiled," FDNY firefighter Jim Lee said.

Firefighters say the 81-year-old man was very thankful that they made it. 

The Red Cross is on the scene working with displaced residents.

Due to the fire, 93rd Street between First and Second avenues was closed.

First Avenue was also closed between 91st and 94th streets with heavy delays reported on the FDR.