Authorities say at least 13 people were killed and dozens injured when a fire broke out at a crowded nightclub in eastern Thailand early Friday morning.

It happened in the Mountain B nightclub in the Sattahip district of the Chonburi province, which is southeast of Bangkok.

The fire broke out around 1 a.m. local time. Thai authorities have not yet determined the cause of the deadly blaze. All victims were identified as Thai nationals. 

One witness named Nana said she was at the venue with her friends when the fire began. 

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Major fire damage at Mountain B pub in Thailand

Over a dozen people were killed and dozens more injured when a fire broke out at Mountain B pub in Thailand. (AP Photo/Anuthep Cheysakron)

"I saw flames above the stage, on the right side. I think it was about the same time as the singer on stage saw it too and he shouted 'fire!' and threw the mic at it," she told local TV.

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"I saw a lot of the pub's bouncers covered in fire inside," she added.

Exterior damage from Thailand nightclub fire

Exterior damage from a fire is seen at the Mountain B pub in the Sattahip district of Chonburi province in Thailand. (AP Photo/Anuthep Cheysakron)

Video from local TV showed people fleeing the fire as workers attempted to quell the flames. Several people's clothing was on fire as they emerged from the pub. Footage also captured shoes and bottles strewn across the ground.

A DJ at the pub told reporters that he heard the sounds of an explosion and shattering windows. 

Thai prime minister asked for increased safety after the deadly nightclub fire

Thai Prime Minister Prayuth Chan-ocha, seen in this 2019 file photo, urged businesses to adhere to safety measures amid the nightclub fire. (AP Photo/Sakchai Lalit)

The pub was lined with flammable soundproofing, and it took two hours for firefighters to put out the blaze.

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Prime Minister Prayuth Chan-ocha released a statement saying authorities would assist the victims' families. He also urged businesses to ensure they have emergency exits and follow proper safety procedures.

Associated Press contributed to this report.