RIO DE JANEIRO, Jan. 3 (Xinhua) — At least 60 people were killed in a prison riot which lasted 17 hours in the northern city of Manaus, authorities said on Monday.

The riot occurred in the Anisio Jobim Prison Complex, the largest prison in the state of Amazonas. State Public Security Secretary, Sergio Fontes, said in a press conference that the death toll was "between 50 and 60" . This was later revised to at least 60.

Twelve prison wardens were taken hostage, but all of them were released uninjured, according to Epitacio Almeida, representative of the local barrister association's Human Rights Commission.

Authorities did not release the names of any victims. At least 25 bodies were already taken to the local morgue.

A judge in Amazonas, Luis Carlos Valois, who accompanied the negotiations with inmates to end the riot, told the press that many of the 60 dead were executed on Sunday.

Daily O Globo quoted him as saying that "piles of bodies were scattered along the corridors, severed limbs in the corners and decapitated heads around the place. The floor was awash with blood."

In the beginning of the riot, on Sunday afternoon, inmates threw six headless bodies out of the prison.

Brazil's prison system is notoriously overcrowded, which has led to several deadly riots in the past. The Anisio Jobim prison was reportedly overcrowded, with the daily Folha de Sao Paulo reporting in October 2016 that the prison had 585 inmates, but capacity for only 454.

This time, the riot seemingly began as a fight between members of two rival crime organizations: Primeiro Comando da Capital (PCC) — a drug gang from Sao Paulo, which expanded to other states, and Familia do Norte. According to a statement by public security officials, most of the dead appeared to be PCC members.

"This was yet another chapter of the silent and merciless war of drug trafficking that is scattered all over the country," said Fontes.

There have also been reports of inmates breaking free of the prison but these remain unconfirmed so far.