A series of overnight attacks on Sao Paulo police stations left 30 people dead and 29 injured, in apparent reprisal for the transfer of gangsters to a high-security prison, officials said.

The onslaught began at 2300 GMT and ended early Saturday after 23 police officers, five assailants and two civilians were killed in 55 attacks on installations and individual police officers, authorities said.

Five assailants were killed in the attacks believed to have been organized by the First Capital Commando, Sao Paulo's biggest mafia organization, sources said. At least 16 suspects were arrested.

President Luiz Inacio Lula da Silva, attending a summit of European and Latin American leaders in Vienna, said he asked Justice Minister Marcio Thomaz Bastos "to do everything necessary not only to end the rebellion in Sao Paulo but, moreover, to avoid additional crimes and deaths."

The gangs were thought to be angered with the transfer of 765 inmates to higher-security prisons.

The attacks were carried out against police barracks, militarized police stations and officers on patrol in Sao Paulo and other cities in Sao Paulo state, including Mogi Mirim, Ribeirao Preto, Osasco, Cubatao and Guaruja.

Meanwhile, inmates in at least 22 prisons staged uprisings and took 150 hostages, authorities said. Later, police took control of some prisons, but 98 hostages remained in 16 jails.

Brazil's prisons are notoriously overcrowded and often rocked by violent unrest.

Prisons Administration chief Nagashi Furukawa said the transfer of inmates came on the heels of a careful study of which inmates could be influential behind bars and potentially be involved in uprisings.

The 55 attacks hit police, firefighters, police vehicles, patrolmen and prison officers.

All police vacations and weekend leaves were canceled in Sao Paulo state.

Sao Paulo Governor Claudio Lembo said transferring the 765 inmates would be a difficult task.

"We all knew the risks we are running, but it was necessary. The residents of Sao Paulo can be completely at ease with the experience of the civilian and militarized police," he told reporters.

"Sao Paulo will not be cowed by crime," he said.

The commander of the militarized police, Elizeu Teixeira Borges, attended the same press conference.

"We had information that something like this could happen and we were on alert since Thursday," he said. "The number of deaths could have been much higher had it not been for that alert."

PHOTO CAPTION

A group of policemen give information to a passer-by in the surroundings of an attacked police station in Sao Paulo, Brazil. (AFP)