As many as 25 people are now feared dead following a fire on board a diving boat in the United States.

The boat – named the Conception – was moored just off Santa Cruz Island, nearly 100 miles west of Los Angeles, California.

Some 39 people were believed to have been on board when the fire started.

Nine people remain missing, the US Coast Guard confirmed, while five crew members are known to have survived.

The cause of the blaze is not yet known.

At a news conference, sheriff Bill Brown said coast guard services overheard a mayday call at 03:30 local time on Monday, saying that the boat was engulfed in flames.

Reports suggested some passengers could have been trapped below deck.

Those who escaped the fire may have been sleeping in the main cabin of the boat rather than below.

They were awake and had jumped off the bridge before a vessel called the Grape Escape arrived to rescue them.

Image: Li Ying/Xinhua News Agency/PA Images