The fire was first reported shortly after 5 a.m. at a church building in the 10800 block of S. Broadway Street, according to the Los Angeles Fire Department.
The address came back to Greater New Holy Trinity Missionary Baptist Church.
Responding firefighters found flames coming from the second floor, the department said. Crews operated in the defensive mode.
Video from AIR7 showed that part of the roof had collapsed.
The fire was declared a knockdown just after 7 a.m. Crews will remain on scene to mop up, LAFD said. Arson investigators are on scene, per protocol.
Broadway Street was closed in both directions in the area. Drivers are advised to use alternate routes.
The building was vacant at the time of the fire, fire officials said. They added that there was construction happening on the building. No injuries were reported.
LAFD says the Los Angeles Department of Building and Safety is assessing the heavily damaged church building "to ensure viability and structural integrity."
No further details were immediately known.
The cause of the fire is under investigation.