Fifty-two people were killed yesterday when the Russia-bound bus they were travelling on caught fire in Kazakhstan, the central Asian nation's emergency services ministry said.

"On January 18 at 10:30 am, a bus caught fire ... 55 passengers and two drivers were on board. Five people who managed to escape are receiving medical assistance. The rest died on the spot," the ministry said, without elaborating on the cause of the blaze.

All those who died are believed to be Uzbek nationals, an interior ministry official told Interfax-Kazakhstan news agency. Kazakh media reported they were migrant workers travelling to Russia.

Uzbekistan's emergency services ministry said it had opened a hotline.

The vehicle was registered in Kazakhstan, emergency services ministry official Ruslan Imankulov told AFP. He said the fire spread very quickly.

Regional emergency service officials initially blamed the fire on a short circuit and said the bus was overloaded, Interfax-Kazakstan news agency reported.

Ministry representative Imankulov did not confirm this however, telling AFP: "It's too early to talk about the reasons for the fire."

Panic broke out on board the bus, hindering evacuation, while survivors managed to climb through a door and window, Kazakh news site BNews reported.

Two of the survivors suffered burns to their hands, emergency services officials told AFP, while others suffered minor injuries.