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Mexico City - At least 12 people were killed and eight were injured on Thursday following a head-on collision in southwestern Mexico between a bus and a fuel tanker truck which exploded, seriously burning some of the victims, authorities said.

Rescue workers were still recovering bodies from the crash site and the death total was expected to climb, said a spokeswoman for federal police in Petacalco just inside the state border of Guerrero and neighboring Michoacan.

"Some of them were burned to a crisp," the spokeswoman said.

At least eight people were also injured in the collision, some of them critically, the spokeswoman said.

Police said the bus was travelling to the Pacific coast when it hit the tanker, which had left the Lazaro Cardenas area en route toward the interior of Mexico. It was not immediately clear what had caused the collision, the spokeswoman said.