RIO DE JANEIRO, Brazil (AP) — The snuffing out of the Olympic flame in London today marks a conclusion for most.

But for 2016 host city, Rio de Janeiro, it kicks off four years of pre-games jitters and a race against the clock to ready this notoriously laid-back beach city for the global sports showcase.

Playing Olympic host is a high-stakes bet for any country, but Brazil seems to have more riding on the games than most. The nation has enjoyed an economic surge over the past decade, a boom that saw it overtake Britain as the world's sixth biggest economy. Brazilians regard the Olympics as their grand entrance onto the world stage — and their emergency as a superpower.

Still, observers say efficiency and punctuality have never been the country's strong suit, and many are bracing for a rocky ride as Rio rushes to build the city's four main Olympic sites and undertakes a massive, pre-games infrastructure overhaul.

Rio is also one of 12 Brazilian cities gearing up to host the World Cup football tournament in 2014.

"On the ground, we can expect ... cost overruns and a rush to push through projects. Cariocas (Rio residents) will see their cost of living increase, their streets clogged and the branding of their public spaces," said Christopher Gaffney, an American academic who's a visiting professor at the graduate school of architecture and urban planning at the Fluminense Federal University in Rio's sister city, Niteroi.

His research focuses on preparations for the World Cup and Olympics.

"While the Brazilians will undoubtedly pull together a great party, the hangover will last for a generation," Gaffney said.

More than 230 projects are slated to be finished by the 2016 games with the sports venues scheduled for delivery between mid-2015 and early 2016 for test events, according to the International Olympic Committee. Of those, over 65 have already been completed or are in the final stages.

That leaves a high volume of projects to be carried out simultaneously over the next four years — a feat that even Rio 2016 organisers acknowledge is tricky.

"Time is an adversary but time is also on our side," Leonardo Gryner, CEO of the Rio 2016 organising committee, told reporters at a news conference Friday in London. "We'll get a few cold sweats but this is normal. We are on time and going according to schedule."

Rio 2016 organisers see the games as a pivotal moment in the city's history that will turn the page on the decades of slow decline and neglect that followed the loss of the capital to Brasilia in 1960. Speaking at a recent news conference, Rio Mayor Eduardo Paes promised the event would leave an "enormous legacy."

City, state and local governments are investing nearly US$12 billion in massive infrastructure projects they say will help revitalise derelict urban areas and ease the chronic transportation woes in this metropolis of six million. Beyond the sporting venues, Rio is slated to get a new metro line, a revamped airport, improved roads and a renovated port.