Four bodies have been recovered by rescuers after a horrific blaze tore through a dive-boat anchored off Santa Cruz Island.
The coast guard said the bodies had injuries consistent with drowning.
There are fears that more than two dozen others could have died in the tragedy, aboard the boat named Conception off the Southern California coast.
"Right now they're conducting shoreline searches for any available survivors," Coast Guard Captain Monica Rochester told reporters at a brief news conference at Channel Islands Harbor in Oxnard.
The coast guard said the vessel was believed to have carried 38 people, including five crew members who jumped off soon after the fire ignited before dawn.
"The crew was actually already awake and on the bridge and they jumped off," Captain Rochester said.
Two suffered minor injuries, said Coast Guard Petty Officer Mark Barney.
Captain Rochester said the 75-foot commercial scuba diving vessel was anchored in Platt Harbor, about 20 yards off the northern coast of Santa Cruz Island, when the fire ignited around 3am.
She said the vessel sank in 64 feet of water, adding its bow is still visible above the waterline.
The Conception was on the final day of a Labor Day weekend cruise to the Channel Islands when the fire erupted.
"At 3.15am this morning the Coast Guard overheard a mayday call. The call was garbled, it was not that clear, but we were able to get some information out of it to send vessels on scene," Mr Barney said.
The island is about 90 miles from Los Angeles. One of the crew suffered minor injuries.
Shocking pictures taken by the Ventura Fire department show firefighters battling the blaze.
The Coast Guard had helicopters, small boats and a patrol cutter in the area for a search-and-rescue operation.
The boat was on a Labor Day weekend cruise taking divers to the Channel Islands off the coast of Southern California.
The vessel Conception was operated by Santa Barbara-based Worldwide Diving Adventures, which says on its website it has been operating such expeditions since 1972.
It was outfitted with dozens of small berths for people to sleep in overnight.
