Four bodies have been recovered and four more spotted on the ocean floor after a boat was destroyed by fire off the coast of California, US authorities said. Five crew of the commercial diving boat Conception escaped the blaze. The fire started in the early hours of Monday. The boat was anchored just metres off Santa Cruz Island, about 90 miles (145km) west of Los Angeles. The vessel is now submerged as a search and rescue operation continues. At a press conference, Sheriff Bill Brown said 39 people were on board the vessel when fire broke out. The cause of the blaze is so far unknown. Four bodies have been recovered so far - two male and two female adults - and four more have been spotted on the sea floor, he said. "The boat remains unstable and we are not sure when we will be able to recover those bodies [on the sea bed] and any more that may be in the vessel," he said.

What happened on the ship?

Coastguard services overheard a mayday call at 03:30 local time (10:30 GMT), saying that the boat was engulfed in flames, according to Capt Monica Rochester, the coastguard sector commander for Los Angeles/Long Beach. Reports say some passengers may have been trapped below deck. Firefighters were unable to board the vessel as the flames had already taken hold Those who escaped the fire may have been sleeping in the main cabin of the boat rather than below. They were awake and had jumped off the boat's bridge before a Good Samaritan vessel called The Grape Escape arrived to rescue them. One survivor has minor injuries. Sheriff Brown speculated that oxygen or propane tanks could have exploded during the fire, but there was no sign this sparked the blaze. "Nothing in the [mayday] broadcast from the vessel... indicated there was an initial explosion," he said.

What about those who are missing?

Capt Rochester said the boat was "fully in compliance" with safety regulations, and had no prior violations. She said the search efforts would continue into Tuesday morning, but that "we should all be prepared [for] the worst outcome". Mourners left flowers at the railing of Truth Aquatics, the company that ran the dive tour Sheriff Brown said the fire was "probably the worst case scenario you could possibly have" on a vessel, as it was in open water at night with most people asleep below decks. "Fire is the scourge of any ship," he said. "Of all scenarios... you couldn't ask for a worse situation."

What's the ship like?

The bow of Conception is still sticking out of the water. It sank 20 yards (18m) off the north shore of Santa Cruz Island, at the depth of 64ft (20m). Run by a diving company called Truth Aquatics, which has a 4.5 rating on Trip Advisor, Conception was used for chartered trips in the Channel Islands National Park. It was on the final day of a three day scuba diving excursion for the Labor Day weekend. The boat's layout shows three rows of double bunks with a shower room at the front of the boat. "Pillows, blankets, reading lights, privacy curtain and personal storage are provided," the company's website says.