At least 21 people died and 30 were injured on Wednesday when a tour bus and a semi-trailer collided, and then the bus rolled over and caught fire, on a mountain road in the southeastern Mexican state of Veracruz, officials said.

The bus was travelling from Mexico City to Tuxtla Gutierrez, located in the southern state of Chiapas, when the accident occurred.

Roberto Hernandez, the civil defence director for Nogales township, said the bus turned onto one side and the ground blocked its exit doors.

Initial reports said 20 people were killed, but state civil defence director Guadalupe Osorno said one injured person died later.

Authorities said both vehicles were westbound when they apparently collided in a mountainous area known as Cumbres de Maltrata. Both caught fire.

The cause of the crash is under investigation. 

Getty has reported that the bus was carrying passengers back from a pilgrimage to a Catholic shrine.

In April 2006, a bus carrying religious pilgrims in the same area ran off the highway and tumbled down a steep ravine, killing 65 people.