RIO de Janeiro police announced seven more deaths and 17 arrests as drug-fuelled violence continued to sweep over parts of the city that is to host the 2016 Olympics.

The death toll has risen to 33 since Saturday, when rival gangs began a turf war for control of drug trafficking in several favelas, or shanty towns, located among Rio's luxury hotels and residential areas.

A suspected gang member is arrested in the Morro Santo Amaro slum in Rio de Janeiro. Credit:Reuters

Gangs are suspected of using high-calibre weapons to shoot down a helicopter on Saturday near the Morro dos Macacos favela, which remained the scene of fighting between rival gangs and police trying to subdue them. Three of six police on board died.

Most of the dead this week were suspected gang members, but the victims also included several bystanders. On Wednesday, 18-year-old student Jose Carlos Guimaraes was seriously wounded in the abdomen by a stray bullet,