MEXICO CITY:  At least 12 people were killed and up to 30 were injured when a bus plunged some 90 metres (300 feet) off a roadside in a mountainous region of southern Mexico near the Guatemalan border, authorities said on Sunday.

The accident occurred near the town of Motozintla when the bus ferrying people home from a spiritual retreat on the Pacific coast came off the road and fell down a steep slope, emergency services in the state of Chiapas said in a statement.

The passengers come from the nearby municipality of La Trinitaria and at least 12 died, the statement said. Officials in the area said as many as 30 people were also injured.

It was not immediately clear what caused the accident.

Rescuers were working to free people from the bus, which photographs from the scene showed had been reduced to a mangled wreck in a wooded gully.