A notorious Brazilian criminal gang has unleashed a second wave of attacks against police, bringing to at least 52 the number of people killed in what one official called the deadliest assault of its kind in Brazil’s history.

A wave of attacks on police by a notorious gang has killed at least 30 people - including 23 officers – in the bloodiest assault of its kind in the history of Brazil’s largest state, authorities said.

Brazil's most notorious organised crime group has led uprisings in five prisons leaving at least seven dead.