Between 30 and 50 people died Thursday in a prison fire and riot in the northern Mexican industrial city of Monterrey, local media reported.
Authorities in Nuevo Leon state have not yet provided information about the number of people who died - possibly including both inmates and prison officials - or were injured in the incident.
Meanwhile, two employees of the Topo Chico prison, where the riot occurred, told EFE the death toll was nearly 60.
The riot reportedly was triggered by an attempted prison break by inmates belonging to the Los Zetas drug cartel, as one group of prisoners set a fire to distract the guards while other inmates tried to flee.
The uprising apparently occurred after the Zetas were stripped of their control of the penitentiary.
Local media said several inmates managed to escape, although the precise number is unknown.
The riot began early Thursday at Topo Chico, the oldest prison in Nuevo Leon. Three hours later, authorities were trying to bring it under control by deploying members of the army, Civil Guard and the Monterrey police.
Eyewitnesses cited by local media said inmates' screams and grenade blasts were audible from outside the penitentiary, while security forces sealed off the perimeter to prevent a massive prison break. EFE