BANGKOK - At least 17 people were killed when a bus hit a tree in southern Thailand Friday, police said, suggesting that the driver had fallen asleep at the wheel.

About a dozen other passengers were injured when the bus, part of a convoy of 12 vehicles, ran off the road at dawn in southern Krabi province on its way from central Samut Prakarn to the southern province of Phang Nga, they said.

"As of now 12 people died at the scene and five more have died in hospital, but many of those who are wounded are in a serious condition," said police commander Colonel Thakoon Netpukana.

"I'm sure that the accident was caused by the driver falling asleep. The road is flat and straight," he said.

More than 40 people had been travelling in the bus, which was completely destroyed by the crash, he said.