Monica Villamizar reports from Alemao amid the fighting as police close in on drug gangs.
Police in the Brazilian city of Rio de Janeiro have claimed victory in the Alemao shantytown after launching an operation aimed at pushing members of a drug gang out of the area.
But about 600 gang members are believed to be remain in Alemao, a grouping of a dozen slums in the north of the city where tens of thousands of people live.
"There is no doubt that Rio residents have reason to celebrate today," Rodrigo Oliveira, Rio police inspector, said. "The complex was seen as a fortress for drug traffickers and in less than two hours we took control.''
Al Jazeera's Gabriel Elizondo, reporting from Rio, said that the first phase of the operations was over, with security forces having penetrated deep into the slum.
"Authorities are planning to put a Brazilian flag on top of the favela," our correspondent said.
"This is our D-Day," Colonel Lima Castro, the military police spokesman, said in a reference to the historic allied invasion of Normandy during World War Two.
Brazilian police seized 40 tons of marijuana in its crackdown on drug trafficking gangs in slums, in northern Rio de Janeiro, a state official told the AFP news agency on Sunday.
"The military police alone seized 20 tons. The rest was done by the civil police force and other security forces that participated in the crackdown," said a spokesman for Rio de Janeiro state's security.
Secretariat Reporters were shown several houses where huge quantities of marijuana, ready packaged for distribution, were stacked in rooms and abandoned by drug traffickers fleeing security forces.
Nelson Jobim, Brazil's defence minister, had authorised the deployment of 10 military armoured vehicles, two air force helicopters and 800 soldiers for the offensive, to reinforce the 17,500 police involved in the earlier stage of the crackdown. About 300 federal police were also dispatched to bolster local forces.
Police had given suspected drug traffickers in Alemao slum an ultimatum to turn themselves in after more than 1,000 police and army personnel surrounded the area.
Ahead of the offensive, many residents of Alemao streamed down the narrow alleyways of the slum carrying their belongings - chairs, washing machines, bags of clothing - to escape being caught in the crossfire.
The crackdown on traffickers in Rio de Janeiro's shantytowns, locally known as favelas, has resulted in the deaths of at least 45 people and the arrest of 192 others since it began last week.
Security forces launched the operations after a week of intense and widespread violence in the city, during which dozens of motorists were robbed and more than 100 cars and buses were set ablaze.
Authorities say the gangs are protesting against a two-year-old police campaign that has pushed the criminals out of slums where they have long ruled with impunity.
Brazilians have been glued to the continuous coverage of the violence on local television, which has shown buses engulfed in flames and elite police units battling their way through the slums.
Sergio Cabral, Rio de Janeiro's governor, has vowed repeatedly to break the back of drug gangs in the shantytowns.
"We have demonstrated to those who don't respect the law ... the pre-eminence of a democratic state governed by the law," he said after police occupied Vila Cruzeiro, a slum neighboring Alemao.
Around two million of Rio's inhabitants – one-third of the population – live in more than 1,000 slums. Authorities hope to pacify 100 of the most violent ones by 2014 when the country will host the football World Cup.