At least eight people were killed and authorities fear the death toll could be as high as 34, after a diving boat caught fire Monday morning off the coast of Santa Cruz Island, north of Los Angeles, officials said.

Four bodies had been recovered after the 75-foot commercial vessel called the Conception, carrying 33 passengers and six crew, went up in flames about 3:30 a.m., officials said.

Four more bodies have been found on the ocean floor but could not be immediately recovered, Santa Barbara County Sheriff Bill Brown said Monday afternoon at a news conference.

Five crew members, who were awake and above deck on the bridge of the ship, jumped off and were rescued by a "good Samaritan" recreational vessel called "The Grape Escape," U.S. Coast Guard Capt. Monica Rochester said.

Thirty-four of the 39 aboard the boat were sleeping below deck when the fire broke out, Rochester said.

Planes and ships will continue to scour the coast looking for survivors, but Rochester said she fears the worst.

"We will search all the way through the night, into the morning but I think we should all be prepared to move into the worst outcome," Rochester said.

A 75-foot vessel burns during a rescue operation off Santa Cruz Island, California, on Sept. 2, 2019. Santa Barbara County Fire Department / Reuters

Brown said he still holds some hope.

"We're always hopeful that there would be more survivors found ... doing everything we can to see if anyone could have survived this," the sheriff said.

The National Transportation Safety Board said the agency was sending a team to investigate.

The Conception, operated by Truth Aquatics out of Santa Barbara, was in full compliance with safety and licensing standards, Rochester said.

Bob Hansen told NBC News that he and his wife were in their boat The Grape Escape in a cove about 400 yards away at the time of the fire and were awakened by someone banging on their boat and yelling. Hansen said the couple found the captain and four crew members who arrived in a dinghy that was towed by the Conception.

Hansen said the Conception was “fully engulfed” by fire.

“It's a 75-footer and the flame was from one end of the boat to the other. There wasn't a blank spot on it and probably 30-foot flames,” he said. “I mean, it was just totally on fire.”

One of the crewmen had what appeared to be a broken leg, and another said his girlfriend was on board and did not make it off, Hansen said. Some were crying. They were clearly distraught, he said.

“They felt so helpless. They said that with everything — so much on fire so much that they just couldn't get to them,” Hansen said.

The Coast Guard told two of the able-bodied crew members to return in the dingy with a flashlight to look for survivors, he said.

Hansen said that the crew told him that to get out, the passengers would have had to go through the galley, which was completely engulfed and where the crew believes the fire began. The crew said when they opened the door, ceiling tiles were on fire and falling down and a second exit was blocked, Hansen said.

Sheriff Brown said the timing of the fire and the ship's location contributed to the tragedy, with flames breaking out as almost everyone on board was sleeping.

"To be in a remote location, have a fire that occurs, have limited if any firefighting capability that could address ... you couldn't ask for a worse situation," he said.

So far, there's no immediate evidence of criminal act, authorities said.

Rescuers don't yet know how they'll get inside the burned out vessel.

"It's upside down in relative shallow water with receding tides that are moving it around," Sheriff Brown said.

"So at some point, they're going to have to make a determination when the best time is to ... either re-float that vessel and attempt to recover anyone inside or to try to make the recovery while it's still on the ocean floor."

The boat was scheduled for a three-day $665 diving excursion "to explore the pinnacles of San Miguel Island" that departed Saturday morning and was due back Monday evening, according to a Truth Aquatics schedule.

"The beginning of September is the best time to be at San Mig, which see strong winds and swell during much of the year," the online description of the trip said.

The boat, which launched in 1981, had a 46 bunk occupancy, rafts and jackets for 110 passengers and was equipped with food preparation appliances, including a built-in Bar-B-Que.

Hansen, of The Grape escape, wishes they could have done more. He said that he was told there were three birthday parties on the vessel over the weekend, including a 17-year-old girl who was on the trip with her parents.

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The Coast Guard received a mayday call that the "vessel was engulfed in flames" about 3:30 a.m., Rochester said.

Firefighters also rushed to the scene of the dive boat at 3:28 a.m., the Ventura County Fire Department said in a tweet. Crews from the Santa Barbara Fire Department and Ventura County Fire Department were fighting the blaze when the boat sank 20 yards off shore in 64 feet of water, the Coast Guard said in a statement.

Santa Cruz Island is part of the Channel Islands National Park, off the coast of Ventura. Officials said the area has strong currents, and the waters in the part of the Pacific Ocean are cold even in late summer.