Fifteen people are dead and 18 others injured after a tour bus crashed in eastern Gangwon Province on Wednesday afternoon.

Police say the bus lost control and plunged 15 meters down a hill in Pyeongchang, some 120 kilometers west of Seoul.

Eyewitnesses said the bus swerved off a winding downhill road after shaking violently for nearly 30 seconds and hitting a roadside tree.

Police suspect malfunctioning of the brakes or the bus driver's carelessness might have caused the accident.

Most of the passengers were elderly people in their 60s. The bus was returning to Seoul after a trip to scenic eastern mountainous areas.