The fire started at about two o'clock in the area of Maple and Turner in East Central Fresno.
Investigators are still trying to determine what caused the large fire to break out in the abandoned warehouse.
The flames sent thick plumes of black smoke into the sky that could be seen across the city.
Firefighters say the warehouse was mostly empty, but there appeared to be pressurized containers inside the building, which added to the fire.
The fire broke out just before students were released at nearby Leavenworth Elementary.