Some 21 people were burned to death in a crash involving a cargo truck and inter-city passenger bus in central Mexican state Queretaro, the state's Public Security Secretariat (SCC) said on Monday.

The crash took place at 1:30 a.m. local time (0630 GMT) on the road linking Queretaro and neighboring state San Luis Potosi.

The secretariat said that the bus, belonging to the Omnibus de Mexico company, hit a tanker truck carrying chemicals, leading to an explosion and fire that engulfed both vehicles. There were no survivors.

The bus had left Mexico City bound for Zacatecas, a state further north. The SCC said that the bus driver probably fell asleep at the wheel.