Image caption The wreckage of the bus was badly charred by the fire

Nineteen people have been killed in a collision between a bus and a lorry in central Thailand, reports say.

At least 20 more people were injured in the incident, which took place in Saraburi province early on Tuesday.

The double-decker tour bus - which was travelling from Bangkok to Roi Et in the north-east - burst into flames after the collision.

It was not immediately known how many people were on board the bus. A police investigation is now under way.

All of those who died were on the bus, Thai newspaper The Nation said.

The accident happened around 05:00 local time (22:00 GMT) when the lorry veered across the road and hit the bus, the Bangkok Post said.

"The truck crossed from the opposite lane of traffic and hit the bus," said local police officer Lieutenant Colonel Assavathep Janthanari, according to AFP news agency.

Police have arrested the lorry driver, reports say.

A pick-up truck behind the bus was also reportedly involved in the collision.