Number One, a well-known nightclub in Krabi, caught fire at about 5.30am on Tuesday. The popular club was closed at the time and nobody was inside.
The fire started in the DJ booth before spreading to the walls and air-conditioning vents. It took firefighters about 20 minutes to extinguish it.
The security guard, Bandit Rakkij, 52, said he was sitting in front of the club when the owner, who had been watching remotely via CCTV, called and told him there was a fire inside the building.
The guide went inside and used a fire extinguisher and some water to try in vain to stop the fire from spreading. The blaze took hold very quickly, so he called for help.
Police said they presumed the cause of fire was an electrical short circuit, as they found scorch marks on a control panel in the DJ booth. A forensic team went to the scene for further investigation.