The notorious organised crime gang known as the First Command of the Capital (PCC) is now targeting police stations Brazil's most populous state.
Officials said the faction’s onslaught is apparently in reprisal for the transfer of jailed gangsters to a high-security prison.
At the same time, many people have been taken hostage in uprisings in at least 18 prisons.
The Sao Paulo prisons syndicate said about 250 guards have been taken hostage in the past 48 hours, while local media said 130 remain held by prisoners on Sunday.
State prison affairs secretary Nagashi Furukawa said prisoners are holding over 174 hostages including prison employees and visiting families, in rebellions underway in 17 prisons.
The dead include 35 security guards and police, and 14 suspected gang members, as well as three civilians, according to the Sao Paulo state government.
Police said they have arrested 17 people in connection with the attacks, according to CNN.
As well as in the city of Sao Paulo, attacks have taken place in the suburbs of Osasco, Guarulhos and Carapicuiba, and in the coastal cities of Cubatao and Guaruja.
Battle of wills
The attacks and revolts have been described as Sao Paulo's biggest wave of organised violence.
The PCC, the state's largest criminal gang, apparently carried out the attacks after 765 gang members were transferred to higher security facilities deep in the state's interior, in a bid to isolate jailed gang leaders.
The transferees included Marcos Wilian Herbas Camacho, aka Marcola, considered the gang's chief.
This conflict is part of an ongoing battle of wills between Sao Paulo authorities and the PCC.
Founded in 1993, the gang was responsible for uprisings in 20 prisons in February 2001.
It has also been involved in drugs and arms trafficking, kidnappings and bank robberies.
In November 2003, the gang attacked more than 50 police stations, killing three police officers and wounding 12.
The PCC initiated a new round of violence at the beginning of this year. In January there were six attacks against police stations, leaving three officers dead.
On April 8 four more officers were killed in more attacks.
It is widely understood that prisons in Brazil are controlled by criminal organisations and not the government.