An early morning fire Friday roared through a garage that had been converted into living space, killing two young sisters and critically injuring a third.

Firefighters found the three girls unconscious in a tiny back bedroom and not breathing after the blaze was reported around 2 a.m., Fire Chief Dave Ellis said.

Stephanie Aviles, 6, died, along with Jasmine, 10, authorities said. Their 7-year-old sister, whose name was not immediately released by authorities, was in critical condition at Long Beach Memorial Medical Center.

The girls' 17-year-old sister fled the burning home for help shortly after 2 a.m. and then went back but the flames kept her from entering, Fire Chief Dave Ellis said.

"The fire was blowing out both the front door and the windows," Ellis said.

The teen, who was not injured, was baby-sitting because the children's mother, who is single, was at work, police Detective Richard Birdsall said. He didn't know where she was working.

About half of the four-car garage had been converted into living space, with a living room, a kitchen area and a tiny bedroom. Investigators said there were no smoke detectors.

Authorities said a cheap space heater was plugged into a power strip, but were not sure whether the strip was overloaded or whether an electrical short sparked the blaze, fire Capt. Mike DuRee said.

The building was uninsulated and temperatures had dipped into the 40s, authorities said. The garage had its own address but it was unclear whether the building had been legally converted, DuRee said.

The bedroom, about the size of a walk-in closet, was gutted in the blaze. A white teddy bear in a Santa hat was on the floor, the price tag still attached. Outside the building were three little plastic toy cars.

Jose Perez, who lives in the front home with his family, said the family in back was related to his wife and was only spending the night in a sleepover, but fire officials said they were living there.