The bus was travelling along a road in Kazakhstan’s north-western Aktau region that links the Russian city of Samara to Shymkent, a city in southern Kazakhstan close to the Uzbek border.
It was unclear in which direction the bus had been travelling, but the route is widely used to transport Uzbek migrant workers to and from Russia where they often work on building sites.
57 people were on board, all of whom are believed to be Uzbek nationals.
Only five people managed to escape the burning vehicle, the interior ministry’s emergencies department said on Thursday.
The ministry said the apparent accident had happened at 10.30am local time (0430 GMT), but provided no details about its cause.
A photograph posted online from the site showed the bus completely burnt out, Reuters reported.
Video footage also showed it positioned diagonally across a two-lane road in the middle of a snow-covered steppe, in flames and emitting heavy black smoke.