At least 52 inmates have been killed in a pre-dawn Mexican prison brawl, as prisoners fought with blades, bats and sticks and ignited a fire in the overcrowded jail.

Key points: Mexico prison riot leaves dozens dead

Mexico prison riot leaves dozens dead Angry family members protest outside jail

Angry family members protest outside jail Riot occured on the eve of Pope Francis' visit

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 between leaders of two rival groups, including one led by a member of the Zetas drug cartel, Mr Rodriguez said.

"They used sharp weapons, bats, sticks," the governor said, adding that the 60-year-old prison houses 3,800 inmates, twice its capacity.

Angry relatives flocked to the prison and tried to force their way in, desperate for information about loved ones caught in one of the deadliest Mexican prison riots in recent years.

Security forces are deployed outside the Topo Chico prison. ( AFP: Julio Cesar Aguilar )

During the brawl, inmates set a fire in a supply room. TV images showed flames coming out of the prison in the middle of the night.

Mr Rodriguez told a news conference that the clash erupted before midnight on Wednesday (local time) and that authorities brought it under control at 1:30am on Thursday.

"We are experiencing a tragedy stemming from the difficult situation that they are living through at penitentiary facilities," Mr Rodriguez said.

"We can confirm the deaths of 52 people ... The process of identifying victims continues," he said, adding that all the victims were male inmates.

Five of the injured inmates were in serious condition.

Mr Rodriguez rejected speculation that women or children may have been inside at the time of the riot.

Troops and federal police were deployed inside the prison to keep it under control.

Mr Rodriguez said no inmates escaped and no firearms were used.

Desperate relatives protest

Riot police and ambulances were deployed to the prison while dozens of relatives threw rocks and pulled the gate open as riot police blocked their way.

Other relatives shouted through a fence, hoping to hear information from the inmates.

Some relatives of prisoners formed a line by holding hands to block a boulevard.

"We will stay here blocking this avenue until they give us an answer," Ernestina Grimaldo, whose son is a prisoner, said.

"We want to know how our relatives are doing because they are telling us that there are more than 50 dead and no authority is giving us answers."

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.

Mexican jails are notoriously overcrowded and massive prison breaks have taken place in recent years.

In February 2012, 44 inmates were killed and another 30 escaped from another Monterrey prison, known as Apodaca.

AFP