The death toll has risen to at least 19, with up to 30 more missing, after fire tore through a casino-hotel complex in a Cambodian town on the Thai border.

About 400 employees and patrons were in the Grand Diamond City casino and hotel in the town of Poipet when the blaze broke out around midnight Wednesday (local time), leaving the building charred and gutted by Thursday afternoon.

Cambodian police said hundreds of military, police and volunteer rescue personnel had joined the rescue effort, which was suspended at nightfall given the risk the building might collapse.

Sek Sokhom, head of the Banteay Meanchey provincial information department, said the number of deaths could exceed 20, with 60 people injured.

Neighbouring Thailand sent firetrucks to help fight the blaze in a bustling border region.  Photo: AAP

Videos posted on social media on Thursday showed people falling from a roof after they were trapped by the fire at the Grand Diamond City casino and hotel in the border town of Poipet.

Many of those inside, both customers and staff, were from neighbouring Thailand.

In a video posted by Cambodia’s firefighting agency, onlookers could be heard shouting pleas to rescue people trapped on the roof of the hotel complex, which is more than a dozen stories tall at its highest point. The video showed at least one man falling as the flames reached the roof.

“Oh, please help rescue them. Pump water … pump water,” shouted the onlookers.

The Department of Fire Prevention, Extinguishing and Rescue posted that calls for help were heard from the 13th, 14th and 15th floors at 4am and hands were seen waving from windows as well as a mobile phone’s flashlight signalling from inside the complex.

“The fire was massive, and was inside the casino, so it was difficult for our water cannons to reach it,” observed a firefighter on the video posted online by the fire department.

He said that was the reason the fire continued burning for such a long time.

The fire took 14 hours to put out.  Photo: Getty

The blaze, which started around midnight Wednesday, was finally put out at 2pm on Thursday, said Sek Sokhom, head of Banteay Meanchey’s information department.

He said a local Buddhist temple was being prepared to receive the dead.

The number of deaths appeared likely to rise, as more bodies of those trapped inside were discovered and critically hurt people succumbed to their injuries.

Banteay Meanchey police chief Sithi Loh said 360 emergency personnel and 11 firetrucks had been sent to the scene of the fire, whose cause was not yet known.

People walk under a destroyed part of the Grand Diamond City hotel-casino. Photo: Getty

“I don’t think there will be any survivors because of very thick smoke. Even we all (the rescue staff) have to wear proper gear when we go inside the building, otherwise we cannot breathe at all,” said Montri Khaosa-ard, a staff member of Thailand Ruamkatanyu Foundation, a social welfare organisation that sends volunteers to the sites of emergencies.

Thai and Cambodia rescue teams work side by side

Thailand’s public television network, Thai PBS, reported that 50 Thais, both staff and customers, had been trapped inside the casino complex.

It reported that Cambodian authorities requested help to deal with the fire from Thailand, which sent five firetrucks and 10 rescue vans.

The Cambodian government has set up a committee to investigate the cause of the fire, which remained unclear, he said.

A key part of Cambodia’s tourism industry, casinos in the capital of Phnom Penh and on the borders with Vietnam and Thailand are a draw for visitors from Asian nations that ban gambling.

Those in Poipet are hugely popular with short-term Thai visitors as gambling is illegal across the border and unlicensed casinos operate underground there.

Many of the victims were Thai nationals, rescue workers said.

“(The deceased) that we found are Thais, as their IDs show.

The bodies now have to be identified,” said 53-year-old rescue worker Somboon Kwanoum.

Punnawat Promsri, 40, said her Thai relative died trying to help two women escape the fire.

“Max stayed behind to help one woman and a pregnant woman escape,” she told Reuters. “I saw from a video clip, I think it was him.

He hung on to a rope attached to a fire basket and it broke.

He didn’t die from fire or smoke.”

Crowds of onlookers had gathered nearby during the day and ambulances rushed to and from the scene as bodies were pulled from the smouldering ruins of the building, according to Reuters witnesses and footage broadcast on local news.