At least 17 persons have been reportedly killed and 31 others critically injured after a bus plunged down from above 90 metres off a mountainous roadside in southern Mexico.

According to emergency services in the state of Chiapas, the immediate cause of the accident which happened near the town of Motozintla, near the Guatemalan border has not been ascertained.

A spokesperson for the emergency services, Daniel Cuate  told newsmen that the bus was ferrying passengers from the nearby municipality of La Trinitaria on the Pacific coast after a spiritual retreat when it skidded off the road and crashed down a steep slope.

Mexican president, Enrique Pena Nieto has since extended his condolences to the bereaved families via his Twitter handle.