SAO PAULO, Brazil (CNN) -

A prison riot turned deadly in the southern Brazilian city of Cascavel when rioters killed at least four fellow inmates, according to police in Brazil.

Two inmates were decapitated, while two others were thrown off the roof of a cell block, said Maria Carle, spokeswoman for the Justice Secretariat of the state of Parana.

The raging riot "erupted on Sunday with prisoners overpowering guards," said Carle.

Authorities say hundreds of prisoners are demanding better living conditions and more flexible visiting hours.

On Monday, prison rioters held numerous inmates and two guards hostage as negotiations for their demands continued.

The prison housed just over 1,000 inmates and around 150 have been transferred since the rioting started, according to local media reports.

Prison riots are not uncommon in Brazil, often sparked by overcrowding, poor conditions and rivalry between criminal gangs.