At least 15 people were killed on Friday when a passenger bus plunged into a ravine on a highway in western Guatemala, rescue officials said.

Leandro Amado, a spokesman for volunteer firefighters, told reporters that the victims included 11 men, three women and a minor, while about 20 injured people were taken to nearby hospitals.

The bus fell into a ravine about 75 metres deep, and the cause of the accident remains unknown.