The tragedy occurred at Na Ladprao eatery near Soi Lat Phrao 1 Road at 12:02am when many people were inside. Firefighters brought the blaze under control in about half an hour, according to the Department of Disaster Prevention and Mitigation (DDPM).
The fire killed 27 people and injured 63 others, reports the Bangkok Post. The dead victims comprised nine men and 18 women. Of the 63 injured, 22 were seriously wounded.
Prime Minister Anutin Charnvirakul, Bangkok governor Chadchart Sittipunt and DDPM director-general Teerapat Kachamat were among senior officials at the scene.
Anutin, also the interior minister, said most fatalities resulted from smoke inhalation. He quoted musicians at the eatery as saying that the fire started at a circuit breaker on the stage in the restaurant, followed by a blackout and an explosion.
Mr Chadchart said that flames spread rapidly through decorations on the ceiling of the eatery and toxic smoke from the burning decorative materials harmed victims.
He said that the eatery was licensed with music performances allowed inside and officials concerned had inspected it in April.
Suriyachai Rawiwan, disaster prevention and mitigation director of Bangkok, said there were fire exits at the rear of the venue and victims apparently rushed to toilets at the back of the premises where rescuers had difficulty reaching them.
The identification of the bodies is continuing.