At least 21 people were killed and another 30 injured after a tour bus rolled over and caught fire following a collision with a semi-trailer on a mountain road in the Mexican state of Veracruz.

When the bus turned onto one side, passengers were unable to use the exit doors, Roberto Hernández, civil defense director for Nogales township, told the Associated Press.

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Firefighters work at the site of a deadly road accident between a bus and a semi-trailer, on a mountain road in Veracruz state, Mexico, on Wednesday. (Civil Protection Office of Veracruz via AP)

Authorities said both vehicles heading west when they crashed in an area known as Cumbres de Maltrata. The truck also caught fire.

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In 2006, 65 religious pilgrims died in the same area when their bus ran off the highway and tumbled down a steep ravine.

The Associated Press contributed to this story.