A British tourist is missing after a fire broke out on a diving boat off the island of Koh Tao in Thailand.

Alexandra Clarke, 26, a backpacker from London, was reportedly in the bathroom at the back of the boat when a blaze ignited from the engine of the wooden vessel at 9.15am local time on Sunday.

There were 22 people aboard the boat, named Davy Jones Locker, 16 of whom were tourists, according to officials.

Fifteen tourists were evacuated to another boat, along with two crew members and four diving instructors and assistants.

Photos from the scene show large plumes of smoke billowing across the sky, as neighbouring boats watch on. After the fire was extinguished, the authorities conducted a thorough search and discovered one person was missing.

The boat was reportedly transporting tourists from Koh Tao to a diving site at Southwest Pinnacle, and the exact cause of the fire remains under investigation.