Thai authorities are investigating whether negligence was what led to the deadly inferno at a Bangkok bar late on Sunday, as survivors reported doors being locked and the lack of signage demarcating emergency exits.

The use of flammable materials as decoration may have facilitated the rapid spread of the fire, which originated near the stage, police say.

This "indicates a lack of caution and disregard for the safety of the patrons," Police General Kittiratt Phanphet said on Monday.

The blaze has left at least30people dead and dozens more injured. First responders found many of the victims in the restrooms at the end of the bar, from where experts believe they tried to flee – but couldn't.

As of Tuesday morning, 27 of the deceased victims have been identified, authorities said. More than 70 people are injured, 24 of them critically.

Preliminary investigations suggest the blaze was caused by a short circuit in an air conditioner, which quickly cut power throughout the bar.

But several people who had visited the bar earlier have described it as a dark room even in its original state. Phatsara Khamloet, who visited in May, told BBC Thai she had to navigate a "winding route" to reach the bathroom, and noted that the exits were not well marked.

Busakorn Saensuk, a fire safety expert from the Engineering Institute of Thailand who inspected the aftermath at Rong Beer Na Lat Phrao, said the door near the restrooms was locked, while the two doors at the entrance were partially obstructed by furniture and other objects.

Customers would instinctively have run away from the fire, towards the back where the restrooms were, Busakorn tells BBC Thai.

"But once they reached the back, they couldn't get out.

"If the emergency signs were lit, people would have been able to see how the door was locked and may have been able to unlock it," she says.

Busakorn also noted that the stage was decorated using highly flammable materials such as plastic flowers, while the ceiling was plastered with combustible foam.

Survivors have described the stage being engulfed in flames within seconds. Thai indie band Thotsakan, which was performing when the fire broke out, has lost two members to the tragedy.

Worsak Kanok Nukulchai, a professor specialising in structural engineering, believes many people would have died by inhaling toxic smoke "even before getting burned".

The first flames would have reacted with the flammable materials to produce carbon monoxide and hydrogen cyanide, often known as the "toxic twins" of fire smoke, he explains.

The bar was registered as a "restaurant with live music" rather than an "entertainment venue", Bangkok authorities have confirmed, and it was therefore not required to use fire-retardant materials.

Bangkok's Metropolitan Administration says it is reviewing regulations governing the materials allowed in the construction and decoration of entertainment venues and restaurants alike.

According to PBS Thai, the owner of Rong Beer Na Lat Phrao previously owned another pub in Thailand's Yasothon province, which was also destroyed by fire in December 2019.

There were no casualties in the earlier incident because the blaze happened during the day, the report said.