More than 50 people were killed in a bloody prison riot in the Amazon jungle city of Manaus, a Brazilian security official told the Globo TV network on Monday.

Sergio Fontes, the head of security for Amazonas state, told Globo he fears that more dead will be found as authorities get a clearer idea of the extent of the rebellion that began late on Sunday, sparked by a fight between rival drug gangs, Al Jazeera reported.

Brazil's overcrowded prisons routinely witness riots breaking out, with similar incidents reported in October.

In the latest riot, a group of inmates exchanged gunfire with police and held 12 prison guards hostage late on Sunday in the largest prison in Manaus, an industrial city on the banks of the Amazon River, Globo TV reported.
 

Brazil has the fourth largest prison population behind the US, China and Russia.

Horrific conditions and inter-gang violence were seen in many facilities, some of which are essentially run by drug gang leaders who continue to run their criminal enterprises in and outside despite being locked up.