The fire was reported around 2:30 a.m. on Sarah Street, according to the Los Angeles Fire Department.
Officials say a working smoke alarm alerted the people inside the home about the fire. By the time firefighters arrived, an 80-year-old and a 35-year-old man who managed to escape the flames were already outside the home, but two others were still trapped inside.
Firefighters rescued an 83-year-old man in serious condition with minor burns and a 50-year-old woman in grave condition.
There were also numerous animals inside the home. Fire crews pulled a dog from the flames and were seen administering oxygen to the animal at the scene. The dog recovered a short while later, but three cats who were also inside did not survive.
The cause of the fire is under investigation.