A tour bus carrying schoolteachers in northeastern Thailand plunged off a mountain road Friday, killing at least 17 people, police said.

About 30 others including the bus driver were injured in the crash, said police Lt. Chinnadet Deetae from the Chiang Mai police force.

Most passengers on the bus were teachers and their family members who were taking a trip to the Royal Flora Ratchaphruek 2006, an international horticultural show in the northern city of Chiang Mai.

Initial investigations indicated that the vehicle's brakes had jammed, and that the driver had been unable to slow down along a mountain road.

The bus skidded before it flipped over and then plunged about 33 feet into a river, Chinnadet said.