The search for 34 people who are presumed to be dead after a diving boat caught fire off the coast of Santa Cruz Island, was called off Tuesday morning, according to the U.S. Coast Guard.

The 75-foot commercial vessel called the Conception, carrying 33 passengers and 6 crew members, went up in flames at about 3:30 a.m. Monday, officials said.

"It is never an easy decision to suspend search efforts," U.S. Coast Guard Capt. Monica Rochester said during a Tuesday news conference. But no signs of distress had been found during the 24-hour-long search and "we should all be prepared to move into the worst outcome," she said.

Crews would turn their focus to recovery and investigation to find out "why this incident occurred and what we can learn from this tragedy," Rochester said. Investigators would also be interviewing the five crew members, including a boat captain, who survived the blaze.

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When asked if the called-off search was an indication that the Coast Guard believed everyone on the boat but the five crew members who escaped were dead, Rochester said: "That would be a correct assumption."

The remains of 20 people — 11 women and 9 men — had been recovered, Santa Barbara County Sheriff Bill Brown said during the latest news conference. Between four and six additional bodies were seen trapped within the wreckage of the boat, but divers were unable to recover them Monday night and would try again Tuesday if they can stabilize the sunken boat and break through the wreckage, Brown said. Divers were working in waters with a depth of 65 feet.

He said authorities were in contact with families of 30 of the victims, and were collecting DNA samples from them to identify remains. "Many, if not all of the victims will need to be identified through DNA analysis" because the bodies had suffered extreme thermal damage, Brown said.

Earlier, Coast Guard Lt. Cmdr. Matthew Kroll said that crews collected what appeared to be the bodies of 25 people. He said that figure needed to be confirmed by the coroner and "the numbers may change slightly."

Five of six crew members, who were on the third deck of the ship when the fire broke out, jumped off and were rescued by a "good Samaritan" recreational vessel, Rochester said Monday. She said Tuesday that the crew's quarters are on the top deck, so it was "perfectly normal" for them to be there.

The other crew member was among the 34 who are thought to be dead and were sleeping below deckwhen the fire broke out. It's unclear if the victims woke up and tried to escape the flames, or perished in their sleep, Rochester said.

Coast Guard crews launched seven missions that covered 160 miles in the search for survivors that began early Monday morning, she said.

Former Truth Aquatics crewman James Miranda prays and drops flowers into the water after 25 people died aboard a diving boat that caught fire early Monday morning. MARK RALSTON / AFP - Getty Images

The Conception, operated by Truth Aquatics out of Santa Barbara, was in full compliance with regulatory requirements, Rochester said Monday. The Coast Guard inspects vessels like the Conception annually.

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

Truth Aquatics is a Santa Barbara Harbor-based operation that has been in existence since 1974.

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 helped the captain and four crew members who managed to escape.

Hansen said 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. They were clearly distraught, with some crying, 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.

Santa Barbara County Sheriff Bill 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 and then to have all of a sudden a fire that spreads very, very rapidly, you couldn't ask for a worse situation," he said Monday.

The vessel sank about 20 yards from the shore four hours after the fire started.

Officials said Monday they were in discussions about how to handle the wreckage — whether it could be towed without breaking apart or should be examined on site.

So far, there's no immediate evidence of a criminal act. The National Transportation Safety Board sent a team to investigate.

Santa Barbara County said Monday that names of the victims were being withheld pending notification of kin. Many of the victims were from the Santa Cruz and San Jose Bay Area, officials said.