(CNN) Twenty-one people were injured after an explosion and fire on board a ship at the US Naval Base in San Diego, US Navy officials said. The ship could burn for days, "down to the water line," San Diego Fire Chief Colin Stowell told CNN's Erica Hill Sunday afternoon. Officials called for San Diego Fire Department's assistance about 9 a.m. local time, Muoz told CNN. The USS Bonhomme Richard is an amphibious assault ship, according to the US Navy. There were 160 people on board when the fire started, according to the Naval Surface Forces.