Alejandro Vázquez Mellado, head of civil defense for the township of El Marques, said several of the 17 injured were in critical condition. Queretaro state interior secretary Guadalupe Munguía later said the death toll had risen to seven, The Washington Post reported.
The town is in Queretaro state north of Mexico City.
Photos of the scene showed the crumpled wreckage of the bus tossed to one side of the tracks. The vehicle was apparently dragged about 50 yards (meters) along the tracks.
Such accidents are frequent at railroad crossings in Mexico that lack signals or barriers.
MP/PR