Rio de Janeiro: Jailed members of Brazil's most powerful drug gang have killed 33 inmates at a prison, decapitating and cutting out the hearts of most of them, in revenge for a separate prison massacre that left 56 dead this week.

Friday's massacre in the Monte Cristo prison in the Amazonian state of Roraima carried out by members of the First Capital Command (PCC) gang sparked concerns that months of violence between criminal groups controlling Brazil's prisons was spiralling out of control.

The PCC itself was targeted on Sunday in neighbouring Amazonas state in Brazil's worst prison slaughter for more than two decades.

In a mobile phone video that circulated widely on social media, self-described PCC members are seen hacking away at bodies littering an outdoor patio inside the prison.

"You killed our brothers, didn't you? Look here, look what is going to happen you! This is revenge for what you did to our brothers," a PCC member is heard saying on the video as dozens of bodies lie in thick pools of blood.

State officials said the riot in Roraima's largest prison was brought under control by elite police forces. Violence between rival drug gangs there had already led to 10 deaths in October.

Roraima's top security official Uziel de Castro blamed Friday's violence at the state-run prison on the PCC.

He later added that it was believed most of the inmates killed Friday were not members of the group responsible for this week's attack on the PCC in Amazonas and indeed had no gang affiliations.

Justice Minister Alexandre Moraes insisted that the government had control over Brazil's prison system - the fourth largest in world and home to more than 620,000 inmates.

Reuters