Hundreds of people are believed to have been inside the Grand Diamond City hotel-casino, located within sight of Poipet town on the Thai border, when the blaze broke out around 11:30 pm local time on Wednesday.
Photos and videos from the scene showed people huddling on windowsills, with a rescuer telling AFP he witnessed people desperately jumping from the roof to escape the encroaching flames.
“We believe there are many more bodies still trapped inside the compound,” a Cambodian police officer at the site told AFP as rescuers began entering the burned complex.
Local authorities and Thai rescue groups put the toll at 19, with hundreds of Cambodian army and police officers, as well as volunteers from Thailand, helping with the search.
Smoke was still occasionally rising from the complex as rescuers prepared to re-enter the gutted buildings at around 7am.
Many of those injured were taken to Thailand for treatment, with local officials on the Thai side of the border stating more than 50 had been hospitalised, with 13 in critical condition.
The casino is one of many in Poipet, a border town popular with Thais who face strict restrictions on gambling within the kingdom.
Thailand’s foreign ministry said it was working closely with Cambodian authorities to find and identify Thais involved in the incident and was sending “additional equipment, consular officers and police attache” to Poipet.
While Cambodians themselves are unable to gamble, numerous casino-filled hotspots have flourished along the country’s borders with Thailand and Vietnam.
A Grand Diamond City worker, who asked not to be named as it might affect her job, told AFP that she was working on the third floor of the 17-floor hotel wing when the blaze broke out.
“At first, it was not a huge fire,” she said. But she and a co-worker were soon forced to flee outside when the flames began rampaging towards them.
“It [the fire] got huge rapidly,” she said, still in a state of shock over the destruction and death caused by the blaze.
Cambodian Prime Minister Hun Sen today expressed condolences for those who died in the fire, calling it “a tragedy at the end of the year”.
On Thursday, Thai rescuers were forced to call off their efforts as night fell, with an officer from the Ruamkatanyu Foundation explaining conditions were too dangerous to continue.
Around 100 rescuers swarmed the complex throughout the day, some donning heavy protective gear to search the building for survivors - or the bodies of victims.
But they struggled to reach deeper into the casino.
There is no indication as to the cause of the blaze, but it is the latest in a series of fires that have struck popular entertainment establishments in the region.
In August, a fire in a Thai nightclub killed 26 people and injured scores more, while a blaze in a Vietnamese karaoke bar killed 32 people the following month.
Concerns have long been raised over a lax approach to health and safety regulations, particularly in the region’s innumerable bars, nightclubs and other entertainment venues.