CALIFORNIA—An explosion and fire on a San Diego US Naval ship injured 21 people on Sunday, July 12, according to US Navy officials.

A three-alarm fire occurred on the USS Bonhomme Richard, the Naval Base ship in San Diego, as announced by the San Diego Fire Department. According to a tweet posted by the US Navy, 17 sailors and 4 civilians were treated for non-life threatening injuries at a local hospital. The sailors are reported to be in stable condition and all of the crew on the ship has been accounted for.

The fire was reported to have started in the lower vehicle storage area, which was described as “a huge, open area where you store a lot of marine equipment and everything else,” by Rear Admiral Philip E. Sobeck.

It is still unclear what caused the explosion, but initial reports indicate a “sort of a backdraft,” or over-pressurization as the compartment started heating up. According to Sobeck, the ship had approximately a million gallons of fuel. Concerns were raised that the ship could burn for days, but Sobeck assured the public and the sailors that the ship will  likely be salvageable.

The fire was initially reported at around 9 a.m., with two additional alarms being called 9 minutes and 51 minutes after the first. There were a total of 160 people on board when the fire started, according to the Naval Surface Forces. The ship, which has a crew of 1,000, was undergoing maintenance at the time of the fire.