The cause of the fire early on Friday is still unknown and all victims so far have been identified as Thai nationals, police said.
A separate statement from the Chonburi emergency service described 14 of the injuries as severe.
The fire at the Mountain B nightclub, about 180 kilometres southeast of the capital Bangkok, started at about 1am local time, Wuttipong Somjai, a superintendent at a local police station, told Reuters by phone.
Local TV footage showed people fleeing the fire and emergency workers putting out flames and looking through the burnt-out premises, with shoes and bottles strewn across the ground.
A witness who went by the name Nana told local TV she was with five friends when the fire broke out at the venue.
"I saw flames above the stage, on the right side. I think it was about the same time at the singer on stage saw it too and he shouted 'fire!' and threw the mic at it," she told broadcaster PPTV. "I saw a lot of the pub's bouncers covered in fire inside."
The incident comes 13 years after pyrotechnics started a blaze at a New Year's party at the crowded Santika night club in Bangkok, killing 66 people.
Investigations into that fire found several key breaches at the club, official corruption and revealed lax attitudes towards safety at entertainment venues at the time.
Prime Minister Prayuth Chan-ocha on Friday assured victims' families they would receive help from authorities and urged entertainment venues nationwide to ensure they have proper emergency exits and safety measures in place.
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