CALIFORNIA, United States (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 Labour 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.

Brown 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, Brown 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 metres) 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 Harbour on Saturday and the fire broke out about 3:00 am Monday while it was anchored off Santa Cruz Island, about 90 miles (145 kilometres) 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.

Captain Paul Amaral of the vessel assistance company TowBoatUS also launched a fast boat from Ventura Harbour, but it was some 30 miles (48 kilometres) away. By the time it got there around 5:00 am, a Coast Guard helicopter and a fireboat were on the scene.