Gang violence in four prisons in the north of Brazil has left more than 50 people dead over two days.

Key points: Many prisoners were "found dead by hanging inside their cells"

Many prisoners were "found dead by hanging inside their cells" Prisoners were slain in front of visiting relatives a day earlier, an official says

Prisoners were slain in front of visiting relatives a day earlier, an official says Fighting in 2017 left 56 people dead at one of the prisons

At least 42 prisoners were found strangled to death in the jails in the state of Amazonas.

A fight between rival gangs a day earlier at one of the jails, Anisio Jobim Prison Complex in the state capital of Manaus, left 15 dead, authorities said.

A statement from the Amazonas state prison department confirmed the deaths, which were apparently the result of clashes between rival factions.

The department said prisoners were "found dead by hanging inside their cells".

Anisio Jobim Prison Complex was the scene of a riot in 2017 that left 56 dead.

Prisoners were slain with sharpened toothbrushes, according to the BBC.

Amazonas prisons secretary Colonel Marcos Vinicius Almeida said the attacks took place in visiting hours and some prisoners died in front of loved ones.

"It was not a rebellion, it was internal strife," he told the Rio Times.

The department said the situation was "under control" and prisoners were under lockdowns.

Brutal violence between prison gangs is common in Brazil.

The violence often rapidly spreads to other jails, which are typically under the control of drug factions.

ABC/wires