A total of 34 people are believed to be dead from a blaze on a boat off the California island of Santa Cruz, according to local officials, Anadolu Agency reports.

In a press conference late Tuesday, Santa Barbara County Sheriff Bill Brown said the people got stuck on board before abandoning ship when flames blocked their exit from the boat's lower deck, where 33 passengers and a crew member were asleep.

Only five crew members who were sleeping on the top deck managed to escape by jumping off and taking a small boat to safety, according to authorities.

A total of 20 bodies have been recovered, and the boat sank to a depth of 18 meters, Brown said.

DNA samples will be needed to identify the victims, he added. 

It remains unclear what started the blaze, he said, adding that investigation of the fire's cause is ongoing.

Authorities suspended search efforts on Tuesday.

"It is never an easy decision," said Coast Guard Capt. Monica Rochester.

The fire was reported at 3.15 a.m. local time (1015GMT) on Monday.

The 75-foot (23-meter) Conception had been on a Labor Day weekend cruise taking divers to the Channel Islands, an eight-island archipelago in the Pacific.