Masked men entered a bar in Brazil and shot dead patrons in cold blood, in one of 11 seemingly co-ordinated attacks on the outskirts of Sao Paulo overnight.

Eighteen people were killed and at least seven injured in a wave of overnight shootings. Brazilian media reported 11 attacks in total in the cities of Osasco e Barueri​. A 19th death in Itapevi​ was originally included in the toll, but later said not to be related.

Angela Pereira de Souza, whose husband was shot dead in a bar, cries outside a police station in Osasco, Brazil, on Friday. Credit:AP

The victims are all men, aged between 16 and 41, out for a drink or with friends. Reports the victims had criminal records have not been confirmed.

Brazilian Justice Minister José Eduardo Cardozo​ has offered all necessary support to Sao Paulo state to find the perpetrators, after media reports said the massacre could have been carried out by rogue police in retaliation for recent attacks that left a policeman dead.