Riots have broken out in prisons across the Brazilian state of Sao Paulo. A spokesman for the Sao Paulo government's public security office said 14 prisons across the southeastern state had been affected. Carandiru, Latin America's biggest prison, has also been affected with inmates having taken hundreds of hostages.
Unconfirmed reports say some 250 hostages are held by prisoners in Carandiru.
The government is not negotiating.
Carandiru, which is north of Sao Paulo, Brazil's richest and most populous city, was the scene of the country's bloodiest prison rebellion in 1992 when 111 inmates were shot to death when police stormed the penitentiary.
Prison rebellions are commonplace in Brazil where poor treatment of inmates and filthy and overcrowded conditions often erupt in violence. A congressional commission recently described Brazil's prison system as a reinvention of hell .
Local Globo TV reported rebellions in 17 prisons across the state of Sao Paulo in an unprecedented organised show of strength by a criminal organization called the First Commando of the Capital (PCC).
Globo said hundreds of hostages were being held by the nearly 8,000 inmates at Carandiru. The hostages included 45 prison guards, and friends and families of inmates who had come to the huge prison complex for visits.
Local media said prison visitors had been taken hostage in several of the other prisons. The rebellious inmates are reported to be armed with knives and other assorted hand-made weapons.
Globo showed live footage of Carandiru prisoners wandering outside their cells. The words Peace. Justice. Liberty and the number 1533 had been written in huge white letters on the ground between theprison buildings.
The number 1533 is thought to be a signature of the PCC, and corresponds to where the letters appear in the alphabet - the letter P is the 15th letter, the C the third. There is no letter K in the Portuguese alphabet.
Globo said the wave of rebellions was organized to protest a police crackdown in the prison on Friday after five inmates were murdered, allegedly at the hands of the PCC.