MEXICO CITY (AP) — A fiery crash between a tank truck carrying fuel and a passenger bus Saturday has left at least nine people dead in northern Mexico.

Police in the northern border state of Tamaulipas said the collision left both vehicles completely burned. Police photos showed the bus was reduced to a tangle of smoking, charred metal.

The death toll could rise as more charred remains are recovered. The crash occurred before dawn Saturday on a highway that leads to the northern city of Monterrey.

The driver of the fuel truck apparently survived and is under investigation. The bus had apparently set out from the central state of Hidalgo and was headed to Monterrey.

The truck was carrying two fuel tanks in tandem, and such double-container freight trucks have been involved in numerous deadly crashes in the past.

Because weight restrictions and safety inspections in Mexico are lax, there have been calls in the past to ban such extremely heavy and unwieldy trucks.