The Los Angeles Fire Department said the fire broke out at the vacant two-story office building in the 2400 block of West 8th Street at about 7 p.m.
The fire department said 145 firefighters battled the flames in a "defensive operation," attempting to keep the flames from spreading to nearby buildings.
Five people who appeared to be "unauthorized occupants" were in the building at the time of the fire, the fire department stated.
Three of the five people were rescued by firefighters.
According to fire officials, one person was found dead at the scene.
One man, described as a "person of interest," was being interviewed by the Los Angeles Police Department, according to fire officials.
The fire department said the person of interest and one other person were taken to the hospital by ambulance for non-life threatening injuries.
Crews knocked down the fire just after 9 p.m. The cause of the blaze remains under investigation.