At least 20 people were killed and nine injured Thursday when a bus carrying tourists crashed into a petrol tanker in southern Mexico, an emergency services official said.

The crash sparked an explosion that killed the driver of the tanker and 19 people on the bus on a highway in Guerrero state, said Marco Cesar Mayares, secretary of the Guerrero Civil Protection service.

"For the moment we have 20 people confirmed dead, but we are still working to clear the wreckage," he told AFP.

The injured were taken to a hospital in the neighboring state of Michoacan.

Mayares said the bus was carrying tourists from the town of Morelia in Michoacan.