A bus carrying a church group plunged into a deep gorge in the southern Mexican state of Chiapas Sunday, killing at least 17 people and injuring 31, authorities said.

The bus fell into a 90-meter (300-foot) gorge in the Motozintla region near the border with Guatemala, according to the local office of the Interior Ministry's civil protection department.

"At this time, we have registered 17 people who unfortunately lost their lives," the agency said in a statement.

The bus was carrying members of the Seventh-day Adventist Church returning from a retreat in the Pacific coast town of Pijijiapan, local police said.

An apparent mechanical failure caused the accident, according to federal highway police involved in the rescue effort.