The 23-metres-long diving boat 'Conception' suffered a major fire at about 3:15 a.m. on Monday, while moored just off the shore of Santa Cruz and sank.

As of Tuesday, 20 badly burned bodies - 11 female and 9 male - had been recovered from wreckage, while another 14 people are considered dead as a result.

The fast-moving flames are believed to have trapped the passengers who were sleeping at that time in the vessel's lower decks.

Only five people are known to have survived, including the boat’s captain and four crew members, who were on deck and escaped on an inflatable boat.

The single crew member who did not survive may have been sleeping below deck with the passengers at the time.

It is yet to be determined what caused the fire. A team of federal investigators on Tuesday promised a probe into the incident.

California emergency workers have deployed a DNA analysis technique used in war zones and crime scenes to identify the badly burned remains of the victims, Reuters reported.

The same DNA analysis tool was instrumental in identifying victims in the Camp Fire, the deadliest wildfire in US history that killed at least 85 people about 175 miles northeast of San Francisco in 2018.