Guards held hostage in riot at Brazil's Guarapuava jail.

Prisoners involved in the riot have taken to the roof of the jail

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A group of Brazilian prisoners are holding 10 guards hostage to protest over conditions at the Guarapuava jail in the southern state of Parana .

The inmates overpowered and seized 13 guards during a riot on Monday.
They have since freed three of them, and negotiations are under way to have the remaining hostages released.
Jail riots are relatively common in Brazil, which has the world's fourth largest prison population - 500,000 inmates in jails meant to hold 300,000.
Deadly uprisings It is not clear how many prisoners are involved in the riot at Guarapuava prison, but the authorities said there were 30 ring leaders.

They are demanding better food and medical treatment and a general improvement in prison conditions.
Television images showed the inmates on the roof of the prison holding the guards, whom they had stripped of their clothes.
At least five inmates and one guard have been injured in the riot, which started when the prisoners were about to be taken to a construction site to carry out some building work.
The prison, which holds 240 people, allows inmates to study and carry out work projects. Prison authorities said it was the first riot since it had opened 15 years ago.
The inmates released an injured guard shortly after the riot began.
A second was freed in exchange for food, while the reasons for the release of the third have not been made public.
Prison riots in Brazil often turn extremely violent. Five people were killed in August in a riot in Cascavel prison also in Parana, two of them were decapitated.
Earlier this year the UN called for an investigation into the high number of violent deaths in Brazil's prisons, after previous riots at a jail in the north left dozens of people dead.