The operation included officers in helicopters and armoured vehicles and targeted the notorious Red Command in the sprawling low-income favelas of Complexo de Alemao and Penha, police said.
The police operation was one of the most violent in Brazil's recent history, with at least one human rights organisation calling for an investigation into each death.
Rio's state Governor Claudio Castro said in a video posted on social platform X that 60 criminal suspects were "neutralised," 81 arrested and 75 rifles seized during the one-day raid that he called the biggest such operation in the city's history.
An Associated Press journalist saw the bodies of at least two police officers among 10 bodies brought to the Getulio Vargas hospital in Penha. Police did not immediately confirm the deaths of officers.
César Muñoz, director of Human Rights Watch in Brazil, called Tuesday's events "a huge tragedy" and a "disaster."
"The public prosecutor's office must open its own investigations and clarify the circumstances of each death," Muñoz said in a statement.
Footage on social media showed fire and smoke rising from the two favelas as gunfire rang out. The city's Education Department said 46 schools across the two neighbourhoods were closed, and the nearby Federal University of Rio de Janeiro cancelled night classes and told people on campus to seek shelter.
Suspected gang members blocked roads in northern and southeastern Rio in response to the raid, local media reported. At least 70 buses were commandeered to be used in the blockades, causing "significant damage," the city's bus organisation Rio Onibus said.
Governor Castro, from the conservative opposition Liberal Party, said the federal government should be providing more support to combat crime — a swipe at the administration of leftist President Luiz Inácio Lula da Silva.
Gleisi Hoffmann, the Lula administration's liaison with the parliament, agreed that coordinated action was needed but pointed to a recent crackdown on money laundering as an example of the federal government's action on organised crime.
Rio has been the scene of lethal police raids for decades. In March 2005, some 29 people were killed in Rio's Baixada Fluminense region, while in May 2021, 28 were killed in the Jacarezinho favela.
Sociologist and public safety expert Luis Flavio Sapori argues these kinds of operations are inefficient because they don't tend to catch the masterminds, but rather target underlings who can later be replaced.
"It's not enough to go in, exchange gunfire, and leave. There's a lack of strategy in Rio de Janeiro's public security policy," Sapori said. "Some lower-ranking members of these factions are killed, but those individuals are quickly replaced by others."
The Marielle Franco Institute, a nonprofit founded by the slain councilwoman 's family to continue her legacy of fighting for the rights of people living in favelas, also criticised the operation.
"This is not a public safety policy. It's a policy of extermination, that makes the everyday life of Black and poor people a Russian roulette," it said in a statement.
