The Brazilian military launched a pre-dawn crime crackdown in various favelas across Rio de Janeiro on Saturday.
The newly launched Operation Onerat aims to tackle violent gangs operating in the city.
Footage from the Globo news network showed armed soldiers frisking residents and checking vehicles.
Last month the government deployed more than 10,000 soldiers and police on the streets. A crime wave has hit Rio since Brazil's financial crisis.
The operation seeks to reduce citywide robberies and crimes related to drug-trafficking.
Five favelas were targeted by the combined forces of the military and police, the Rio state security service said in a statement.
These were Lins, Camarista Meier, Morros de Sao Joao and Engenho Novo in the north, and Covanca in the west.
Residents posted on social media about waking up to the sound of gunfire and helicopters.
President Michel Temer has signed a degree allowing the military deployment to carry on until end of the year. He said this may later be extended throughout 2018.
"We are going to stay in place until the goals are met," Defence Minister Raul Jungmann said in an interview with Globo. "It could be 24 hours, over the weekend, three days, 15 days. The goal, as always, is the one we said before, to block organised crime, to create a surprise effect."
The state security service said some roads were blocked and the airspace for civilian flights has been restricted over the sectors where the armed forces are operating.
Rio experienced a previous military crackdown on crime ahead of the Rio Olympics, which began exactly a year ago.
However, the retreat of the security forces after the event led to crime increasing again.