The cause of the fire was under investigation. Jackson didn’t know where on the 840-foot amphibious assault vessel the explosion and the fire occurred.

U.S. Pacific Fleet Naval Surface Forces tweeted that 18 sailors “have been transferred to a local hospital with non-life-threatening injuries,” adding that 160 were on board at the time of the explosion.

Images of the fire initially showed a huge plume of dark smoke visible around San Diego. The city is the home port of the Bonhomme Richard, which was undergoing routine maintenance at the time of the fire.

Jackson had estimated that about 200 sailors and officers were on board Sunday morning, which is fewer than if the ship was on active duty.

The ship has the capacity to deploy and land helicopters, smaller boats and amphibious vehicles.