Rescuers scoured the charred ruins of a Cambodian hotel and casino complex on Friday as the death toll from a fire that forced people to jump from windows rose to 25.

Hundreds of people are believed to have been inside the Grand Diamond City venue, located in the town of Poipet within sight of the Thai border, when the blaze broke out late on Wednesday night.

"The death toll now is around 25," said Sek Sokhom, director of the information department for the province of Banteay Meanchey, adding that some of the bodies recovered were found in stairways.

Grieving families have said they were struggling to comprehend the scale of the incident, with one mother saying she was unable to eat because she was so "overwhelmed" by the loss of her 23-year-old son.

Photos and video from the scene showed people huddling on windowsills to escape the flames, with one rescuer saying he saw people desperately jumping from the roof as the blaze inched closer.

A Cambodian police officer told AFP they believed "there are many more bodies still trapped inside" as rescuers began entering the gutted complex.

Hundreds of Cambodian soldiers and police officers, along with volunteers from Thailand, are taking part in the search.

Smoke was still occasionally rising from the complex on Friday as rescuers prepared to enter the buildings at around 7am, with fire trucks on standby at the scene.

Jakkapong Ruengdech, a team leader with Thai rescue group the Poh Teck Tung Foundation, said they needed to establish if there was still intense smoke or fire inside.

Another rescuer from the group, who asked not to be named, described the building as "unstable" and said the search would have to proceed with caution.

Many of the injured have been taken to Thailand for treatment, with local officials on the Thai side saying more than 50 had been hospitalised, with 13 in critical condition. (AFP)