'Five passengers received medical assistance.
The interior ministry did not provide more details about the suspected accident.
Kenes said the "preliminary theory" of investigators about the cause of the fire was a "short circuit".
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.
According to the emergency ministry of Kazakhstan, 55 passengers and two drivers were on board the bus when it caught fire.
A view shows a burnt-out bus in which people travelling on a route used by migrant workers heading to Russian Federation died in a fire, in the Aktobe region, Kazakhstan January 18, 2018. "Another 52 people died on the spot", he said.
According to the Aktobe region's department for emergencies, all the dead are citizens of Uzbekistan.
The vehicle was registered in Kazakhstan, emergency services ministry official Ruslan Imankulov told AFP.
Kazakhstan's latest official statement said the bus could carry up to 59 passengers. Two bus drivers are among the survivors of the blaze, Imankulov confirmed.
January 18: A bus burns on a road in near the village of Kalybai in Kazakhstan. A photograph taken later showed the vehicle completely charred.