Tim Szymanski, a spokesman for Las Vegas Fire and Rescue, said the parents jumped -- the mother suffered a broken ankle -- and an 11-year-old girl who detected the fire grabbed her 1-year-old brother and fled the apartment, the Las Vegas Sun reported.
The 11-year-old suffered burns on her arms and the 1-year-old had burns on his legs and torso, Szymanski said. They were taken to University Medical Center for treatment.
Fire crews were called about 3:10 p.m. Monday to the fire, which began in the storage room of a second-floor apartment, Szymanski said.
Szymanski said neighbors had gathered around the burning apartment and encouraged the parents to jump.
The sixth member of the family, an 8-year-old boy, was walking home at the time of the blaze and saw fire engines and ambulances responding.
A pet dog died in the fire.
The Red Cross is assisting the family, whose apartment was destroyed, as well as six people living on the first floor whose apartments were damaged by smoke and water.
The fire, which caused an estimated $50,000 in damage, is under investigation, Szymanski said.
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