Media playback is unsupported on your device Media caption California residents mourn victims of a boat disaster

Californian officials have begun the process of identifying the victims of a boat fire that is suspected to have claimed 34 lives.

Santa Barbara County Sheriff Bill Brown said that DNA samples would be required from the families of presumed victims to identify them.

Authorities have moved from search-and-rescue operations to a recovery effort. Only five people survived, all crew.

The scuba-diving boat caught fire on Monday as passengers slept below decks.

Twenty bodies - 11 females and nine males - have been recovered but more remain in the submerged wreckage, officials said on Tuesday.

Image copyright Getty Images Image caption People have left flowers at the dock where the Conception is based

Divers will attempt to stabilise the 75ft-long (23m) vessel, the Conception, to recover the remaining victims.

The vessel is upside down in more than 60ft of water, officials said.

When asked why DNA material would be necessary, Sheriff Brown told reporters it was an "inordinately hot fire and the bodies do exhibit signs of extreme thermal damage".

According to preliminary reports, Sheriff Brown said, a 17-year-old and several people in their 60s were probably aboard the recreational diving vessel when it caught fire.

Image copyright EPA/SANTA BARBARA COUNTY FIRE HANDOUT Image caption The boat was totally engulfed in flames as crews tried to rescue those onboard

No cause of the fire has yet been determined.

What have authorities said?

Search-and-rescue operations were suspended on Tuesday morning after a reconnaissance aircraft flew over the wreck and found "no additional signs of distress or debris", Captain Monica Rochester of the US Coast Guard said.

The debris field spanned nearly 1.5 miles (2.4km), said Sheriff Brown. More than 160 miles of ocean were also searched, he added.

The boat had an "open berthing" plan, Cpt Rochester told reporters, meaning there were no locked doors onboard and curtains were used to section off different compartments, such as the sleeping quarters.

Image copyright Getty/Ventura Country Fire Department Image caption Firefighters were unable to board the vessel to put it out as flames has already taken hold

She added that smoke detectors and fire-fighting systems were required to be on the boat, which had passed its most recent annual screening.

When asked if the crew were required to post a night watch, Capt Rochester said that matter was still under investigation.

How did the crew survive?

Five members of the boat's crew escaped the blaze and were able to steer another vessel to a nearby boat, the Grape Escape, where they called emergency services for help.

The captain appears to have jumped into the water with others fleeing the burning boat, Sheriff Brown said.

The Conception was split into three decks, he said, with the passengers being given the bottom level as their chambers.

The middle deck housed the boat's galley and salon, and the top deck was the crew's quarters and the boat's bridge, he added.

He said it was "perfectly normal for the crew to be up on that assigned deck" and closest to an exit when the fire broke out.

Who was on the Conception?

None of those onboard have been formally identified, but family members have begun releasing the name of missing loved ones:

The brother of one marine biologist - 41-year-old Kristy Finstad - told US media she had been leading a dive trip and was presumed dead

The Pacific Collegiate School in Santa Cruz several of its students and parents had been on the boat. The trip was not part of the school curriculum

St Joseph's Medical Center in Stockton, California, said one of its nurses, Evan Quitasol, had been on the ship, along with her father, Michael Quitasol, a former employee at the hospital.

Another former St Joseph's staff member, Fernisa Sison, was also on board, the hospital said

Susana Rosas, Evan's mother, wrote on Facebook that two of her other daughters had been aboard the Conception. Nicole Storm Solano Quitasol and Angela Rose Solano Quitasol were on a trip with her ex-husband, Michael, and his wife Fernisa Sison, she wrote

On the eve of the disaster, three birthdays - including one for a 17 year old girl - had reportedly been celebrated by passengers on the doomed boat.

Actor Rob Lowe was among those paying tribute to victims, writing on Twitter that it was "an unspeakable horror on a boat I've been on many times".