Footage shared online by first responders shows a huge blaze raging and plumes coming out of the front door of the Na Ladprao pub in the northern part of the Thai capital early on Monday morning.
People are seen trying to flee as thick black smoke billows into the sky.
Rescuers said the fire was reported around midnight.
Thai Prime Minister Anutin Charnvirakul told reporters at the scene that 27 people died and that several of the injured have been taken to the hospital.
He said the cause of the fire is under investigation.
Anutin said a musician who was performing at the pub told him that he saw smoke coming out of a circuit breaker near the stage before the power went out, then an explosion was heard and thick smoke quickly filled the place.
Many of victims were found at the restrooms, at the back of the pub, Anutin added.
Firefighters took about half an hour to bring the fire under control.
Photos of the aftermath show charred tables and chairs, and the damaged interior of the pub.
Thai public broadcaster Thai PBS World reported that at least 30 people were killed in the fire at a packed beer house.
Thailand has been the scene of similar tragedies in the past.
In 2022, 14 people were killed by a fire at a music pub in the eastern part of the country.
And more than a decade before that, 66 people were killed and more than 200 injured in a fire during a January 1, 2009 New Year's Eve celebration at the Santika nightclub in Thailand's capital.
That blaze was apparently sparked by an indoor fireworks display.
with DPA
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