MONTERREY, Mexico - Dozens of people were killed in a prison riot in the northeastern Mexican city of Monterrey early on Thursday, local media reported, just days ahead of a planned visit by Pope Francis to another prison in Mexico’s far north.

Milenio TV said up to 60 people were killed and dozens injured in the predawn riot at the Topo Chico prison. It said relatives of prisoners had heard gunshots in the early hours and that a fire had broken out.

The Nuevo Leon state government said on Twitter the situation had been brought under control and ruled out a prison break but gave no details on what had happened.

Television images showed police vehicles patrolling the streets near the prison. Relatives of inmates shook the prison gates and tossed rocks at guards and police on the other side. “I want to know that my daughter is OK. She is in the infirmary. There are children in there,” one woman said outside the prison as some relatives shouted and cursed.

Milenio reported that inmates’ relatives who had been within the prison’s premises for conjugal visits had seen inmates with burns.

The incident is the latest in a series of deadly riots in recent years to rock the country’s overcrowded prisons, which often house inmates from different drug gangs.

In 2013, at least 13 people were killed and 65 injured in a prison riot, which was blamed on gang violence, in the central Mexican state of San Luis Potosi.

In 2012, at least 44 inmates died in a Nuevo Leon prison when members of the notorious Zetas drug cartel plotted with prison guards in an elaborate escape.

Pope Francis is to begin his first visit to Mexico as pontiff on Friday. Next week, he will visit a prison in the border city of Ciudad Juarez, which was once one of the most violent cities in the world.

Thursday’s riot was a harsh blow to Nuevo Leon, where many were uplifted when Jaime Rodriguez, a blunt, outspoken rancher with a penchant for cowboy hats known as “El Bronco,” or “the gruff one”, defeated President Enrique Pena Nietos ruling party last year to win the governorship.

Rodriguez, a former member of Pena Nieto’s Institutional Revolutionary Party (PRI), waged a campaign that capitalized on widespread disaffection with the established parties. He was the first independent candidate to win such a post in modern Mexico.