At least 49 inmates were killed in a Mexican prison brawl Thursday as rival groups fought with bats, sticks and blades and ignited a fire in the overcrowded penitentiary, authorities said.
Twelve others were injured during the "pitched battle" that lasted 30 to 40 minutes at the Topo Chico prison in the northern industrial city of Monterrey, said Nuevo Leon state Governor Jaime Rodriguez.
The fight erupted following a dispute over control of the prison between two rival members of the Zetas drug cartel, Rodriguez said.
"They used sharp weapons, bats, sticks," the governor told radio Imagen, adding that the 60-year-old penitentiary houses 3,800 inmates, twice its capacity, overseen by 100 guards.
One of the inmates was shot dead by a prison guard who was protecting a group of women, Rodriguez said.
During the brawl, inmates set a fire in a supply room and TV images showed flames coming out of the prison in the middle of the night. Authorities are investigating reports of gunfire.
Milenio TV showed video made by neighbors of a brawl in the prison yard, with one inmate falling to the ground as others beat him with sticks in the deadliest Mexican prison riot in recent years.
Rodriguez had earlier given a death toll of 52 but later revised it to 49.
The riot erupted on the eve of Pope Francis` trip to Mexico, during which he is due to visit another notorious prison, in the northern border city of Ciudad Juarez.
Hundreds of relatives flocked to the prison`s gates to demand information. Some bawled and fainted after officials placed a list of victims on a wall outside.
"All this for a robbery, my son was innocent," a woman cried after seeing her son`s name on the list.
Rodriguez told a news conference that the clash erupted late Wednesday and that authorities brought it under control at 1:30 am Thursday.
"We are experiencing a tragedy stemming from the difficult situation that they are living through at penitentiary facilities," Rodriguez said.
Five of the injured inmates were in serious condition.
Troops and federal police were deployed inside the prison to keep it under control. Rodriguez said no inmates escaped.Nuevo Leon has been the scene of violent turf wars between the Zetas and Gulf cartels for years. The Zetas were behind another Nuevo Leon prison massacre that left 44 Gulf members dead while 30 inmates escaped in 2012.
But Rodriguez said this latest prison battle was triggered by a dispute between rival Zetas members -- Jorge Ivan Hernandez Cantu, alias "El Credo," and Juan Pedro Zaldivar Farias, alias "El Z-27."
Zaldivar, who was transferred to Topo Chico two months ago, apparently wanted to take control of the facility from Hernandez, the governor said.
Ambulances were sent to the prison while relatives crowded at the entrance, throwing rocks and briefly pulling the gate open as riot police blocked their way with a parked vehicle.
Other relatives shouted through a fence, hoping to get information from the inmates.
Authorities allowed family members to go into the prison later in the day to see survivors for a few minutes.
"The main yard is completely burned. The bakery is all black," said Martha, a 22-year-old mother of two who saw her husband. "There are shovels and objects thrown around, yellow tape placed by investigators."
Another woman who declined to be identified said the prisoners were handcuffed and looked like they had been beaten.Around 40 prisoners were moved out of the Topo Chico prison following the tragedy, Rodriguez said.
"It`s one of the most complicated (prisons) and it is in a very complicated area, too. Obviously, we have to look at the future of this prison," he said.
Mexican penitentiaries are notoriously overcrowded and massive prison breaks have taken place in recent years.
Even at the country`s top maximum-security prison, the Altiplano near Mexico City, weaknesses were exposed when drug kingpin Joaquin "El Chapo" Guzman escaped through a tunnel in July. He was recaptured in January.
Ruth Villanueva, an expert at the governmental National Human Rights Commission, said last year that there was a serious crisis at the country`s prisons, with 72 of them overcrowded by more than 20 percent.
President Enrique Pena Nieto`s administration vowed to reform the penitentiary system following Guzman`s escape last year.
Pena Nieto expressed his condolences to the families of the victims of the latest prison massacre.