Police in the Brazilian city of Sao Paolo have been attacked by heavily-armed gang members for a second night.At least 52 people, most of them police and prison guards, have been killed in the worst wave of violence to hit the Sao Paolo state in decades. The bloodshed was unleashed by a powerful criminal gang in retaliation for the transfer of its imprisoned members to a remote high-security jail. A total of 100 attacks have been counted since the gangsters armed with grenades and machine guns first struck on Friday night. Around 14 criminals and a number of civilians have also been killed. Inmates belonging to the notorious First Command of the Capital gang have also rioted in 36 prisons around the state, holding dozens of people hostage. The transfer of convicts was said to have been an attempt to head off a widespread prison rebellion allegedly planned for this weekend.