It is a farewell message Ella Ricketson will never be able to deliver to her brother, Tom, after his overseas holiday ended in tragedy in the Cambodian tourist hub of Siem Reap this week.

Mr Ricketson, 32, from Sydney, was one of five people killed when an electrical fire tore through the Hip Hop Club in Siem Reap City about 2am on Tuesday, local time.

Police said the fire started in the ceiling of the nightclub, which is popular among young Cambodians and has no windows and only one door. The fire spread quickly, making it impossible for the victims to escape.

Mr Ricketson died at the scene, along with three Cambodian women and a Cambodian man.

The Cambodian victims are believed to have been university students aged in their early 20s, Siem Reap City police chief Tith Narong said.

Two other Cambodian women were seriously injured, Mr Narong told The Cambodian Daily.

"The nightclub had no windows and it has only one door, and there were too many electrical wires in the ceiling," he said.

The blaze took hold just as the nightclub was about to close, and about 20 people escaped, Mr Narong said.

Mr Ricketson is believed to have worked with the disabled community in Sydney. He had travelled in Vietnam before arriving in Cambodia late last month.

In Cambodia, he had spent 10 days travelling with his uncle, film director James Ricketson, who directed the 1993 drama Blackfellas.

James Ricketson paid tribute to his nephew online, saying he had the "very great privilege and pleasure" of sharing some of Mr Ricketson's last days with him.

"I find it very difficult, less than 24 hours after Tom's death, to use the past tense, but Tom was a sweet, gentle, kind, loving and generous young man whose shyness hid a gold mine of generosity towards his fellow human beings - especially those who, through no fault of their own, through a genetic throw of the dice, found themselves disadvantaged in the body and culture into which they had been born," James Ricketson wrote.

"A special spirit, was Tom. Is Tom."

Ella Ricketson wrote that she would forever carry with her a photograph of her brother, taken recently at the famous Angkor temple complex.

"Tonight my family's world was shattered in a way that we all dread more than anything else," she wrote.

"Today we lost my darling big brother in an accident in Cambodia. As you who knew Tom know, he was an ever kind, sweet, loving and patient man, and talking to him in recent weeks it was clear that these traits had only deepened with all that he had seen and experienced.

"We as a family are all grieving, but we are still completely shocked and finding it hard to believe that our boy could be gone."

The Department of Foreign Affairs and Trade said it was providing consular assistance to the family of an Australian man who had died in Cambodia.