At least six passengers were burnt to death and a dozen injured early Wednesday when the private-run bus in which they were travelling caught fire in Karnataka, an official said.

The accident took place in Hiriyur (town) in Chitradurga district, about 160 km from here.

"The tragedy occurred around 3 a.m. when the bus from Davangere to Bangalore caught fire and fell into a ditch on the side of national highway four (NH 4)," Chitradurga Superintendent of Police Ravi Kumar told IANS.

Of the injured, five are in a critical condition with severe burns and have been admitted to hospitals.

"Six burnt bodies have been pulled out so far from the bus. A rescue team is searching if more bodies are trapped in the wreckage, as about 30 passengers were travelling and 20 escaped with injuries," Kumar said.

Police registered a case against driver and bus operator under section 304 and are investigating the cause of fire.

"The cause is not yet known as the fire, which appeared to have started in the front portion near the driver seat, spread quickly across the bus trapping the victims. Most of the passengers were asleep when the incident occurred," Kumar added.