SANTA BARBARA, Calif. (AP) - No one likely escaped the flames that tore through a boat packed with scuba divers, with all 34 people sleeping below deck presumed dead during a Labor Day weekend expedition off the Southern California coast, authorities said Tuesday as they called off the search for survivors.

Santa Barbara County Sheriff Bill Brown said no one has been found alive after the fire engulfed the dive boat early Monday. Flames blocked an escape hatch and a stairwell leading to the sleeping area crowded with passengers on a recreational scuba diving trip.

Santa Barbara County Fire Chief Mark Hartwig told reporters that the victims' relatives "will rely on us to do everything in our power to find out happened aboard that vessel in the last moments of these family members' lives. That's our commitment."

Only five crew members sleeping on the top deck were able to escape by jumping off and taking a small boat to safety.

The fire that engulfed the Conception killed all 33 passengers and one crew member who was below deck, the sheriff said. Investigators have not yet determined how the fire erupted.

The bodies of 20 victims have been recovered, and divers have seen between four and six others in the sunken wreckage, the sheriff said. Authorities are trying to stabilize the boat that sank in about 60 feet (18 meters) of water so divers can recover those remains.

Most need to be identified by DNA analysis and officials are collecting samples from family members, Brown said.

One passenger, marine biologist and veteran diver Kristy Finstad, 41, was identified in a Facebook post by her brother, Brett Harmeling of Houston.

"Please pray for my sister Kristy!! She was leading a dive trip on this boat," Harmeling wrote.

The sheriff says the majority of the victims appear to have been from Northern California, including Santa Cruz, San Jose and the San Francisco Bay Area.

The boat had departed Santa Barbara Harbor on Saturday and the fire broke out about 3 a.m. Monday while it was anchored off Santa Cruz Island, about 90 miles (145 kilometers) west of Los Angeles. The crew appeared to quickly call for help.

"The call was garbled, it was not that clear, but we were able to get some information out of it to send vessels," Coast Guard Petty Officer Mark Barney said.

Capt. Paul Amaral of the vessel assistance company TowBoatUS also launched a fast boat from Ventura Harbor, but it was some 30 miles (48 kilometers) away. By the time it got there around 5 a.m., a Coast Guard helicopter and a fireboat were on scene.

Amaral said he first searched the water and shoreline, then turned back to the Conception, which was adrift. He attached a line and pulled it into deeper water so the fireboats could reach it.

"We launched that boat knowing that the vessel was on fire, lots of people aboard," he told The Associated Press.

The five crew members, meanwhile, went on a dinghy to a private fishing boat, The Grape Escape, that was anchored near the north shore of Santa Cruz Island. Two had minor injuries.

That boat's owners, Bob and Shirley Hansen, told The New York Times they were asleep when they heard pounding on the side of their 60-foot (18-meter) vessel about 3:30 a.m. and discovered the frightened crew members.

"When we looked out, the other boat was totally engulfed in flames, from stem to stern," Hansen said. "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."

Hansen said two of the crew members went back toward the Conception looking for survivors but found no one.

The 75-foot (23-meter) 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 west of Los Angeles. The fire broke out as the boat sat anchored in Platt's Harbor off Santa Cruz Island.

The Conception, based in Santa Barbara Harbor on the mainland, was owned by Santa Barbara-based Truth Aquatics, founded in 1974. A memorial outside Truth Aquatics in the Santa Barbara Harbor grew Monday night as mourners came to pay their respects.

Dave Reid, who runs an underwater camera manufacturing business with his wife, Terry Schuller, and has traveled 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."

His wife said Truth Aquatics crews have always been meticulous in going over safety instructions at the beginning of every trip she's been on.

"They tell you where the life jackets are, how to put them on ... the exits, where the fire extinguishers are, on every single trip," said Schuller. "They are the best, the absolute best."

Both said the sleeping area is comfortable but tight, however, with bunk beds stacked next to one another on the lowest deck. Coming up to the top deck to get off requires navigating a narrow stairway with only one exit.

If the fire was fast-moving, Reid said, it's very likely divers couldn't escape and the crew couldn't get to them.

Coast Guard records show all safety violations from the last five years were quickly addressed by the boat's owners. Some violations were 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.

The Conception was chartered by Worldwide Diving Adventures, which says on its website that it has been taking divers on such expeditions since the 1970s.

Andy Taylor, owner of Blue Water Hunter Dive Shop in Santa Barbara, said he discussed dive conditions with several people Friday as they were buying some last-minute things before boarding the Conception. Taylor said he often sends divers to Truth Aquatics for trips and he has friends who have crewed on the Conception.

He said he was on the phone all day Monday as friends checked to make sure he had not been on the boat.

"Right now it's a big question of who was on there and who wasn't," he said. "I'm scared to see the list of names, honestly."