The blaze broke out at a residence in the 800 block of S. Crenshaw Boulevard at about 1:07 a.m., Los Angeles Fire Department officials said.
LAFD spokesman Brian Humphrey said the firefighters were hurt when a section of the ground floor of the residence collapsed.
"Mayday was called, and we immediately went into that procedure. We always have rapid intervention companies standing by so 99 times out of 100 they don't have to do anything, but in this case they gaged," LAFD Capt. Daniel Curry said.
The two injured firefighters were pulled from the rubble in minutes.
One of the firefighters suffered a sprained ankle, and the other was hospitalized with second-degree burns over 10 percent of his body and small burns on his hands, Humphrey said.
The firefighter who suffered a sprained ankle was released from the hospital Wednesday morning, and the second firefighter who suffered burns was expected to be released Wednesday evening.
Over 100 firefighters knocked the blaze down in about 90 minutes.
Investigators say squatters may have been using the apartment when it caught fire.
"We're finding evidence of human activity inside these structures so we believe there were squatters inside. They have hot plates and those types of things, so it's possible. At this time, arson is still investigating what exactly happened," Curry said.
The exact cause of the fire remains under investigation.