BRASILIA: Around 60 people were killed in a prison riot in the Amazon jungle city of Manaus, with decapitated bodies of drug gang members thrown over prison walls, officials said on Monday.

It was the bloodiest violence in more than two decades in Brazil's overcrowded penitentiary system.

The security chief for Amazonas state, Sergio Fontes, told a news conference the death toll could rise as authorities get a clearer idea of the scale of the rebellion sparked by a fight between rival drug gangs.

Fontes told reporters several decapitated bodies were thrown over the prison wall, and most of those killed came from one gang.

"This was another chapter in the silent and ruthless war of drug trafficking," he said.

Pedro Florencio, the Amazonas state prison secretary, said the massacre was a "revenge killing" in a feud between criminal gangs in Brazil.

The riot began late Sunday and was brought under control by around 7 a.m. AMT (1100 GMT) on Monday, Fontes said. Authorities were still counting prisoners to determine how many had escaped, he added, with reports that up to 300 fled.

Just as the riot began in one unit of the Anisio Jobim prison complex, dozens of prisoners in the second unit started a mass escape in what authorities said was a coordinated effort to distract guards.

Overcrowding is extremely common in Brazil's prisons, which suffer endemic violence and what rights groups call medieval conditions with food scarce and cells so packed that prisoners have no space to lie down.

The Anisio Jobim prison complex currently houses 2,230 inmates despite having a capacity of only 590.

Hours after the Anisio Jobim prison revolt ended, prisoners at in an adjoining detention center began a riot and attempted to escape. Authorities said the situation was quickly brought under control.