This U.S. Navy photo released July 13, 2020, shows sailors and federal firefighters battling a blaze onboard the amphibious assault ship USS Bonhomme Richard at Naval Base San Diego, California, July 12, 2020. (Christina Ross, U.S. Navy via AFP)
This U.S. Navy photo released July 13, 2020, shows sailors and federal firefighters battling a blaze onboard the amphibious assault ship USS Bonhomme Richard at Naval Base San Diego, California, July 12, 2020. (Christina Ross, U.S. Navy via AFP)

WASHINGTON - Firefighting teams continue trying to put out a massive fire that broke out onboard a U.S. Navy amphibious assault ship docked at Naval Base San Diego in the U.S. state of California early Sunday.  
 
The cause of the fire is under investigation. An official with the San Diego Fire Department, which is helping fight the fire, said there was an explosion.
 
There were 160 sailors aboard the USS Bonhomme Richard when the fire broke out, according to the Navy, and all have been evacuated. Five sailors are still in the hospital for observation. All are currently in stable condition.  
 
In total, 57 U.S. sailors and Navy civilian personnel have been treated for injuries as a result of the fire, including smoke inhalation and heat exhaustion.
 
The ship was undergoing routine maintenance in San Diego. No ammunition or weapons were onboard, and the ship's fuel was not near the source of the fire, U.S. Navy Rear Adm. Philip Sobeck said during a press conference Sunday.
 
Wasp-class Landing Helicopter Dock ships like the USS Bonhomme Richard resemble small aircraft carriers and are currently the largest amphibious ships in the world. They are designed to allow the U.S. Marine Corps to easily shift their operations between the sea and land.