The fire was reported around 2 a.m. Tuesday on Hollywood Boulevard near Nichols Canyon, according to the Los Angeles Fire Department. Officials said the structure had previously burned.
The large fire sent a plume of smoke into the air and was seen from miles away.
The injured firefighter was conducting a search on the second floor of the building when he fell through, said Captain Cody Weireter. He was hospitalized but is expected to be OK.
Arson investigators responded to the scene to determine the cause of the fire.