At least 57 inmates were killed during a prison riot in northern Brazil on Monday as rival gang factions fought each other, an official said.

Sixteen of the dead were decapitated in the second major eruption of violence to rock the country’s severely overpopulated and deadly prison system in as many months.

Fighting broke out in the Altamira Regional Recovery Center at around 7:00 am (1000 GMT), an official from the Para state government’s penitentiary department told AFP.

Two guards were taken hostage during the hours-long clashes, which were brought under control at around midday. The guards were eventually freed.

Brazilian TV stations showed footage of thick black smoke rising from the prison compound and people sitting on the roof of a building.

Other images showed flames inside a building that almost reached the ceiling and people, apparently prisoners, sitting on the ground outside.

“It is likely that many detainees died from asphyxiation (from smoke),” the government official said.

No firearms were found at the scene, but improvised knives appear to have been used in the turf war, according to a statement issued by the penitentiary department.

Some of the bodies had not yet been recovered due to the heat inside some of the prison structures.

The Ministry of Justice and Public Security said ringleaders of the violence would be transferred to federal jails, which are more secure.

About 311 prisoners were being held at the jail, which the department said was not overcrowded. It reportedly has a capacity for 200 inmates.

An outbreak of violence in the same prison in September 2018 left at least seven inmates dead, local media reported previously. Guards had apparently foiled an attempted prison escape.

In May this year, at least 55 prisoners were killed at several jails in the neighbouring state of Amazonas, violence also blamed on an apparent drug trafficking gang dispute.

Most of the victims were killed by asphyxiation, the state government said at the time.

The federal government dispatched reinforcements to boost security in the jails.

Overcrowded prisons

Brazil has the world’s third-largest prison population after the United States and China, with 726,354 inmates as of June 2017, according to the latest official statistics released this month.

The population is way above the capacity of the nation’s jails, which in the same year was estimated to be 423,242 inmates.

The federal government had been expected to add another 115,000 inmates by the end of 2018, Human Rights Watch said in a recent report.

Around 33 per cent of the prison population is made up of pretrial detainees.