Clashes erupted at about 2 p.m. local time Monday (1700 UTC) when inmates from one wing of the Colonia Agroindustrial prison in the Aparecida de Goiania Complex in the city of Goiania broke into another wing.

Mattresses were set on fire before special police units — the Special Penitentiary Operations Group — were brought in to restore security. The fires burned the bodies of those killed, authorities said.

"It was not an act of escape, it was not exactly a rebellion, but one wing against another," Edson Costa Araujo, superintendent of the secretary of public security in the central state of Goiás, said in a statement reported by the O Estado de Sao Paulo newspaper.

At least two of the people killed were reportedly decapitated. Some 14 people were injured, the Folha dee Sao Paulo newspaper reported, quoting security officials.

Jorimar Bastos, the chief of the state prison guard union, told Folha de Sao Paulo that five prison officers were on duty on January 1 and were responsible for 900 prisoners, the news agency Reuters reported.

About 100 inmates also broke out of the prison and 77 were still at large on Monday evening.

The families of prisoners gathered at the gates of the prison in search of information.

Prisoners try to contact relatives after the clashes at the Colonia Agroindustrial prison

Prisons in a chronic state

Rival gangs often fight for supremacy in Brazil's overcrowded prisons. More than 120 people were killed in 2017 in prison clashes. A year ago, a prison riot at the Anisio Jobim Penitentiary Complex in Amazonas state left 56 people dead.

International human rights organizations have repeatedly denounced the Brazilian prison system as one of the worst and most inhumane in the world, with overcrowding, unhealthy conditions in some prisons , as well as mistreatment and torture.

Human Rights Watch (HRW) said in its annual report that the crisis in the Brazilian penitentiary system is "a tragedy " and that the situation in many prisons is close to the "Middle Ages."

According to the latest data from the Ministry of Justice, the prison population in Brazil reached 726,712, an increase of 104,000 people since 2014, making it the third-largest prison population in absolute numbers in the world, behind the United States and China.

Watch video 00:34 Dozens killed in Brazil prison riot

jbh/se (dpa, AP, EFE)