The fire was reported around 1:30 a.m. at the one-story building on E Manchester Avenue, according to the Los Angeles Fire Department.
After extinguishing the flames that engulfed the structure, firefighters searched through the smoldering debris and found the remains of an adult man. No other people were found.
They also discovered that the "seemingly abandoned building" had a cannabis operation inside, which officials said could've been very dangerous.
"They discovered this cannabis operation, which could've been potentially life-threatening for our firefighters due to the sheer number of cylinders and hazardous materials that are inside," said LAFD Capt. Adam VanGerpen.
"This was a very dangerous situation and it could've been much worse," he said while stressing the fact that the roof collapsed during the firefight.
VanGerpen said the victim's wife warned responding crews that there had been an explosion and believed her husband was still inside. Additional details were not available.
No firefighters were injured. The cause of the fire is under investigation.