MONTERREY, Mexico (AP) — A fire and riot broke out Thursday at a prison in northern Mexico, and local media said numerous inmates appeared to have died.

Rescue workers could be seen bringing injured inmates from the Topo Chico prison in Monterrey, at least some with burns. The number of dead was unclear. Officials of the Nuevo Leon state government declined to make immediate comment, but said they would make an announcement later.

Images broadcast by Milenio Television showed the fire continuing to blaze near dawn, with a crowd of people bundled against the cold gathered outside the prison. Some shook and kicked at the prison gates, demanding to be allowed in.

Witnesses said the fire broke out at about 12:30 a.m. (1:30 a.m. EST; 0630 GMT) amid shouts and sounds of explosions. A thick cloud of smoke rose, apparently from inmates burning mattresses.

Mexico's official National Human Rights Commission reported in 2013 that the country's prison system is plagued by violence and cases of inmate control, symptoms of corruption and lack of resources.

The report, based on visits and interviews at 101 of Mexico's most populated prisons, found that 65 of the facilities were run by inmates, not authorities.

In one of the worst incidents in 25 years, 44 inmates died in a prison massacre in February 2012 in Apodaca, Nuevo Leon. After the incident, three top prison officials and 26 guards were accused of helping inmates escape in the confusion.