Crews responded to the one-story warehouse near Main Street and Imperial Highway shortly after midnight Wednesday, according to the Los Angeles Fire Department.
Firefighters were able to knock down the flames in less than an hour, and then they made the deadly discovery. A man was found inside the building and was "beyond medical help," the department said.
He was not immediately identified, and it's unclear whether he died as a result of the fire.
The cause of the fire is under investigation.