AT LEAST 25 people have died and nine others are missing after a scuba diving boat caught fire and sank off the California coast.

The 75-foot Conception was on a three-day excursion to the chain of rugged, wind-swept isles that form Channel Islands National Park in the Pacific Ocean when the fire broke out around 3am in Platt’s Harbor off Santa Cruz Island.

Five crew members who escaped took refuge on a boat called The Grape Escape, anchored nearby. Two had minor injuries.

The local Coast Guard confirmed last night that 25 people had died in the incident.

Rescuers initially recovered four bodies about 145 kilometres northwest of Los Angeles just off Santa Cruz Island, and 16 others were pulled from the water later in the day.

The Coast Guard said five others have been found but not recovered due to unsafe conditions under the boat, which sank about 18 metres from shore.

Authorities are continuing to search for the nine people still unaccounted for.

The four bodies recovered initially had injuries consistent with drowning, the Coast Guard said. 

It wasn’t immediately clear when the bodies on the ocean floor might be retrieved or when divers could search the boat for others.

Investigators have not yet determined a cause for the fire.

The Grape Escape’s owners told The New York Times they were asleep when they heard pounding on the side of their 60-foot fishing vessel about 3.30am and discovered the frightened crew members. They told the couple they fled when the fire grew out of control.

“When we looked out, the other boat was totally engulfed in flames, from stem to stern. I could see the fire coming through holes on the side of the boat. There were these explosions every few beats. You can’t prepare yourself for that. It was horrendous,” one of the owners said.

“The fire was too big, there was absolutely nothing we could do,” he added.

The Conception, based in Santa Barbara Harbor on the mainland, was owned by Truth Aquatics, a Santa Barbara-based company founded in 1974.

Dave Reid, who runs an underwater camera manufacturing business with his wife, Terry Schuller, and has travelled on the Conception and two other boats in Truth Aquatics’ fleet, said he considered all three among the best and safest.

“When you see the boats they are always immaculate,” he said.

“I wouldn’t hesitate at all to go on one again. Of all the boat companies, that would be one of the ones I wouldn’t think this would happen to.”

Coast Guard records show inspections of the Conception conducted last February and in August 2018 found no deficiencies. Earlier inspections found some safety violations related to fire safety.

A 2016 inspection resulted in owners replacing the heat detector in the galley and one in 2014 cited a leaky fire hose.

Records show all safety violations from the last five years were quickly addressed by the boat’s owners.

Includes reporting by Associated Press