SAO PAULO: At least 19 people were shot dead within the span of about three hours in Brazil's biggest metropolitan area, law enforcement officials said on Friday.

Alexandre de Moraes, the head of the Sao Paulo State Public Safety Department said at a news conference that police are trying to determine if Thursday night's shootings in the suburbs of Osasco, Barueri and Itapevi, on the western outskirts of Sao Paulo, are related.

He said 15 of the victims were shot dead in Osasco, three were killed in Barueri and one in Itapevi. Seven people were wounded and are hospitalised.

The mayor of Osasco, Jorge Lapas, told the Globo TV network the killings may have been in reprisal for the recent shooting deaths of two police officers.

At least 10 of the dead were shot at a bar after hooded men got out of a car and opened fire.

Not far away, one young man was shot outside an ice cream store. In the area, another man was shot by two men riding a motorcycle.

Other shootings took place at five other locales.

Citing witnesses, Moraes said that in at least two instances, gunmen wearing face masks arrived and asked who had criminal histories. Those who said they did were shot.

Globo News television broadcast security camera footage showing a group of masked assailants entering a bar, ordering clients to raise their hands in the air, then shooting them.

“We will investigate if the killings were committed by drug traffickers, by off-duty police officers or were acts of vengeance for the recent killings of two police officers.”