Brazilian police are reporting that four people have been killed and many others injured in a prison riot at a facility in the southern city of Cascavel.

Two of those killed were beheaded, while the other two died after being pushed off the roof of the buildings, BBC reported. The riots have been going on since early Sunday and reportedly involves hundreds of prisoners.

Prison officials and other authorities have been negotiating with the rioters to end the violence but without success to this point. The riot has been fueled by prisoners who are not happy with prison management, food and hygiene.

The violence began when wardens who were delivering coffee to inmates were overtaken by prisoners. Up to 1,000 inmates have been involved in some part of the riot, which has included arson and other destruction.

Some reports suggest that prison gangs may be taking advantage of the chaos within the prison to get even with each other, which could explain the violent nature of some of the murders.

Guards have been able to get inside the prison to retrieve the bodies of the four people that were killed.

"They are using the severed head of one of the prisoners to inflict psychological torture on one of the hostages," said Jairo Ferreira, a lawyer that represents the prison agents' union. "There are scenes of terror inside the jail now."

Media reports in Brazil have shown prisoners on the roof assaulting men who are being held with ropes around their necks, according to AP. The men of the roof waved banners carrying the initials PCC, which is one of the prison gangs.

Family members of the inmates have started showing up outside the prison's gates, hoping to find their relatives safe.

Maria Tereza Uille Gomes, the security secretary of the state that houses the prison, came to Cascavel to take control of the negotiations. Brazil has the world's fourth-largest prison population with somewhere around 500,000 inmates.

For comparison, the U.S. has about 2.4 million people incarcerated, according to government statistics.