Rio marked 1000 days to the 2016 Olympics by starting the impending countdown with a blast, dynamiting the entrance to a tunnel to the new Transolimpica expressway which will link the city centre with future Games sites.

Organising Committee president Carlos Arthur Nuzman and Rio governor Sergio Cabral were on hand to push the button to detonate the blast as the host city took a spectacular step towards launching the 23km-long expressway which will help to link four competition zones.

Organisers say the first ever Games to be held in South America are all about providing the city with a lasting infrastructural as well as sporting legacy and Nuzman warmed to the theme, telling reporters: "This construction is of historic and fundamental importance in providing a legacy for the people."

Brazil has in recent months been racked by protests with many residents of the giant nation of some 200 million complaining that the combined estimated $30bn cost of staging next year's World Cup in 12 cities and the Olympics thereafter is too great to bear and the money would be better spent on social projects.

There are also fears that the country will struggle to revamp sagging infrastructure on time.

International Olympic Committee (IOC) coordination teams have made five visits to Rio already, and recognised steady progress.

But just a month ago Brazilian press reported that a national auditing office check on Games finances showed preparations behind schedule with earmarked state cash largely unspent.

In addition, the Games budget has still to be unveiled.

The original budget at the time of Rio's winning bid in 2009 was $2.8 billion, but many analysts say it is likely to top $4 billion with a capital budget of around three times that.

But Nuzman said Thursday that he was "absolutely confident all the construction projects will be delivered in the expected timespan."

IOC chief Thomas Bach told AFP late Thursday he believed Rio has already come a long way and is optimistic the city will prove an excellent host.

"One thousand days remain until the Rio 2016 Olympic Games begin and young athletes across Brazil and around the world are dreaming about being part of this great celebration of sport," he said.

"The Rio Games have inspired those young sports people, as well as many others, who see and understand the benefits that these Games will bring the citizens of the host city and Brazil long after the 17 days of competition have ended.

"These benefits include improvements in the city in terms of transport, infrastructure and social housing, and a considerable sporting legacy for Brazil.

"The 2016 organisers have already accomplished a lot, with more to come, and we look forward to seeing Rio's project develop, as venues are delivered, test events begin, and the excitement grows across the country, helping to spread the Olympic values even further."

Saturday marks the start of the 1,000 day countdown to the 2016 Games.