A supermarket trolley stuffed with a mutilated corpse, a row of burning buses and a police helicopter lying in tatters on a football pitch were, not surprisingly, the sort of images that were absent from Rio de Janeiro’s candidate file when it applied to host the 2016 Olympics.

But it was these pictures that were splashed across the world’s newspapers and television screens last month, after police clashed with drug traffickers in Rio’s Morro dos Macacos favela. The battles that followed left more than 40 dead, only two weeks after Rio was named as the first South American city to host the Olympic Games.

Police numbers are due to increase sharply over the next three years

The Rio de Janeiro bid committee, which marketed the city as a post-recession tropical paradise, has been keen to allay security concerns after the failure of previous attempts to host the Games.

In this year’s candidate file, the committee outlined government plans to increase the military police headcount from 38,000 to 54,000 over the next three years at a cost of $58m. A further $76m is to be spent by 2011 on training civil police officers throughout the country.

But speaking at the opening of a sports centre in the Mangueira favela last week, President Luiz Inácio Lula da Silva warned there were no quick solutions to the violence. “There are people who think that the [state] governor can put an end to the gangs in a minute. But if it was that easy, the violence wouldn’t have lasted 30 or 40 years,” he told reporters.

Jesuíno Ferreira Santos, a 46-year-old taxi driver who moved to the Rocinha favela from the north-east eight years ago, laughs at the prospect of the government regaining control of the city’s hundreds of favelas before the Olympics opening ceremony. “It won’t even happen in my lifetime,” he says.

However, despite the international interest in Rio’s shanty towns, it is the lack of fundamental infrastructure and the less eye-catching issues of transport networks and hotel rooms that could prove to be the host city’s greatest challenge.

Squeezed on to a narrow strip of land between the Atlantic coast and the forested Serra do Mar mountain range, Rio does not easily lend itself to expansion.

But by 2015, the Games’ organisers say that more than $5bn will have been spent on improving the metro system, renovating the suburban railway system and adding three rapid-transit bus lines to cut through the city’s congested streets. The international airport will also be expanded to handle 10m more passengers a year.

Hotel rooms will also have to be built rapidly – the city does not even have half of the roughly 50,000 that will be needed for visitors. While 13,000 rooms have been secured in the city, a further 25,000 will be built within the Olympic villages, where most of the blocks will eventually be converted into long-term housing. And to accommodate the remaining visitors, six cruise ships will also be docked at the port for the duration of the event.

Rio plans to double its stadium capacity and says it will also spend about $4bn in cleaning up the city’s polluted waters.

Ruy Cezar Miranda Reis, Brazil’s secretary for the 2014 World Cup and the 2016 Olympics, says that whatever changes are made will be for the good of the city. “We considered the creation of permanent benefits for the population and not just for the visitors during the Games,” he says.

The staging of the 20th World Cup two years before the Games will give Rio a chance to trial some of its new developments before thousands more visitors descend on the city.

However, some are sceptical of these promises, given the way the city handled the Pan American Games in 2007. In the eyes of the world, the event passed off without a hitch. But for many Brazilians, it became a source of bitterness and embarrassment after costs spiralled and several long-term projects promised by the government never materialised.

Edmilson Dantas, who coaches the country’s national weightlifting team after competing at three Olympic Games himself, says: “Brazil is not prepared for this and I just hope they control the costs this time.”

He is concerned that any benefits will be felt only within the confines of the city. “It will be great for Rio but what about all the other states?” he asks. “I don’t think it’s going to benefit the country as a whole. And yes, we have some famous footballers and we are strong at volleyball and maybe gymnastics, but Brazil does not have a strong history of sport.”

But for the city of 6m people, which has been in gradual decline since the capital moved to Brasília in 1960, the Olympics are also considered a chance to rewrite the script.

After making Rio’s violent slums famous through his Oscar-nominated film City of God, Fernando Meirelles was chosen to produce Brazil’s 2016 Olympics campaign video. And it was in front of his fresh images of tourist landmarks and smiling children, accompanied by uplifting choral music, that International Olympic Committee members in Copenhagen last month cast their vote for Rio.