The Rescue Centre on Koh Yao Noi receive a call just after 6pm that fire was consuming the speedboat on the water.
No passengers were aboard at the time, but the captain, Sonsak Maikaow, 29, and crew member Weerayut Rumsakul, 28, were badly burned before rescuers could pluck them to safety.
After first aid treatment they were taken to Koh Yao Chaiyapat Hospital in Phang Nga, and later transferred to Vachira Hospital in Phuket for treatment to third-degree burns. A third crew member escaped with minor injuries.
The boat itself was wrecked by the fire. Police are to investigate the cause but were told by the crew that the flames broke out in the engine bay.