Officials are calling a raid into Rio de Janeiro's biggest shantytown a success, after more than 3,000 Brazilian security forces backed by armoured vehicles swept into the neighbourhood Sunday morning.

The first troops moved into the hilltop community of Rocinha just before dawn as black military helicopters hovered overhead.

Down below, elite squads backed by police, soldiers and naval personnel made their move. To further tighten security, authorities had shut down airspace and major highways around the favela.

Rocinha has been under the control of drug traffickers for decades, but the government has promised to secure the area before the city hosts the 2016 Olympics. Rio will also host the final matches of the 2014 World Cup

The head of state security, Jose Mariano Beltrame, called the operation a major success and a big step toward breaking drug traffickers' hold on key parts of Rio.

"We have taken over areas that for 30 or 40 years were in the hands of … a parallel power," he said. "This is a very large area. It's one of the biggest shantytowns in the Americas if not the world. We're returning dignity and territory to people."

Officials said it took just 90 minutes to secure Rocinha. They also overran the adjacent Vidigal neighbourhood.

Police to stay in Rocinha

About 100,000 people live in Rocinha, which is one of the biggest drug distribution points in Rio. The slum straddles a green mountainside above posh neighborhoods.

Law enforcement agents will remain in Rocinha for an undetermined time, said Alberto Pinheiro Neto, head of operations for the military police.

"We are prepared for battle. We're prepared for a war, said Capt. Yerson de Oliveira.

Despite the show of force, officials said they were hoping to avoid a firefight with drug traffickers. They arrested the head of the gang while he was trying to escape in the trunk of a car —and for the past week, they've been announcing their plans, giving gang members and residents ample warning.