A battle between rival groups at a prison near Monterrey in northern Mexico has left 49 inmates dead, BBC News reports.

Nuevo Leon state Governor Jaime Rodriguez said 12 other people were injured in Topo Chico jail after prisoners fought with "sharp weapons, bats and sticks".

A fire was also started in a storage room. Officials say the situation is under control and no inmates escaped.

Crowds of relatives outside the jail blocked roads, demanding information. Some threw sticks and rocks and tried to pull the prison gate open as riot police blocked their way.

The incident comes just days before Pope Francis is due to visit a prison in the northern city of Ciudad Juarez, an area notorious for violence between drugs cartels.

Rodriguez had earlier put the number of inmates killed at 52 before revising the figure down. The reason was not made clear, but several inmates are registered more than once at the prison, with different names.

40 of the 49 prisoners have already been identified.

Rodriguez said the fight had started around midnight and lasted 30 to 40 minutes, during which time the two groups of inmates set fire to a storage area. He said one faction was led by a member of the notorious Zetas drug cartel, Juan Pedro Zaldivar Farias, also known as Z-27.

Rodriguez said the other group was led by Jorge Ivan Hernandez Cantu, whom Mexican media identified as a member of the rival Gulf cartel.

The faction leaders are not among the 40 bodies identified so far.

Rodriguez said security was being beefed up at other prisons and some inmates had been transferred out of Topo Chico. He said that although rioters had not had guns, one inmate appeared to have been shot dead by a guard who was protecting a group of women inmates.

A report by the National Human Rights Commission in 2014 said the Topo Chico prison housed about 4,600 inmates but was only designed to hold 3,635.