The confrontation occurred yesterday on a rural highway. Veracruz state police say they approached a car that was parked suspiciously by the side of the road.
Police said they came under fire from the car's occupants, two men and a woman. All three were killed in the exchange of gunfire.
When they secured the crime scene, police found a second vehicle with three more dead bodies.
Local media reported the suspects had been attempting to dispose of the bodies at a nearby dump, but that could not be immediately confirmed.