MEXICO CITY — A fiery freeway accident involving a tractor-trailer and a bus carrying Catholic pilgrims killed 21 people and injured 30 in the Mexican state of Veracruz on Wednesday, according to the authorities and local news outlets.

The accident occurred shortly after 10 a.m. local time on a principal highway between the cities of Puebla and Orizaba.

The bus was en route to the southern state of Chiapas from Mexico City when it collided with the tractor-trailer, flipped over and burst into flames. Photos and videos from the scene showed the crash site engulfed in a giant cloud of smoke and fire.

The bus was carrying members of a Roman Catholic archdiocese located in the city of Tuxtla Gutiérrez in Chiapas.