At least 49 people were killed and 12 people wounded in a prison riot in the Mexican city of Monterrey, the governor of the northeastern state of Nuevo Leon has said.

Governor Jaime Rodriguez said that fighting broke out before midnight on Wednesday night in two areas of the Topo Chico prison, between a faction of the infamous Zetas gang and another group.

"During the clash several prisoners set fire to the food storage and sleeping areas," Rodriguez told reporters at a news conference on Thursday.

It was not immediately clear how the victims died, but Rodriguez said there was no gunfire.

Al Jazeera’s Adam Raney, reporting from Mexico City, said: "The governor made a point of saying that no one had escaped; that this was not an escape attempt but it was this battle between two groups in the prison."

'People are very agitated'

Images broadcast by Milenio TV showed police vehicles patrolling the streets near the prison after unrest broke out in the early hours of Thursday local time.

Milenio TV reported that relatives who visited prisoners in the jail had heard gunshots and said a blaze had broken out. They also said they had seen inmates with burns and that authorities were hunting for escapees.

Witnesses said the fire started at about 12:30am (06:30 GMT) and appeared to have been extinguished shortly after sunrise, the Associated Press reported.

Earlier, local media had said the casualties included inmates and prison guards. Authorities had earlier put the death toll at 52 but later revised it down.

Families of the inmates rushed to the prison after reports of deaths. Some shook and kicked at the prison gates, demanding to be allowed in.

"Police had to come out in riot gear and push these family members back," Al Jazeera's Raney said.

"People are very agitated," he continued. "Mexican prisons are often corrupt, crowded and very violent places - there's a whole history of protests and riots that get out of hand."

Relatives who visited prisoners in the jail had heard gunshots and said that a blaze had broken out [Daniel Becerril/Reuters]
Relatives of prisoners rushed to the scene following reports of deaths  [Daniel Becerril/Reuters]

Source: Al Jazeera and agencies