The fire was sparked from a mattress shortly before 10 p.m. Tuesday in the 2600 block of South Cloverdale Avenue, officials said. Firefighters quickly knocked it down within 15 minutes.
A 37-year-old man was burned on about 80 percent of his body and was taken to a burn treatment center in critical condition. A mother and two children staying in an adjacent space were able to escape with lesser injuries having only suffered from smoke inhalation.
"I heard screaming and shouting so I came out of my house," said Alejandro Guzman, who tried to help put out the fire with a hose.
Fire officials said the garage did not seem to have functional smoke alarms. About 13 people died in fires this year, many that could have been prevented by smoke alarms, officials said.
In the past few weeks, Los Angeles fire officials have been pushing residents to add smoke alarms to homes. They've been going door-to-door in some neighborhoods handing out free detectors.
"We're able to pass out smoke alarms to them and give them documentation and train them," Battalion Chief Steve Ruda said.