Masked and carrying heavy weapons, the 12 commandos overpowered the jail guards. Police sources speculated that the main purpose was freeing a drug boss who is now the subject of an intense manhunt.
Thirteen of the freed prisoners were recaptured immediately afterwards.
Sao Paulo has been subjected to a series of commando prison raids for months. The union that represents guards and police officers has been threatening for weeks to strike, and has denounced the inability of the government to prevent the raids.
According to media reports, the prison raids have become a lucrative business and are handled by specialized professional gangs who tailor their actions to the client's needs.
The police union has demanded that dangerous prisoners with presumable contacts to the drug Mafia be held in top security prisons, with improved security provisions.
(dpa)