All eyes will turn to Rio de Janeiro on Friday when it opens South America's first Olympic Games against a backdrop of political and economic crises off the sporting field and doping scandals on it.

More than 10,000 athletes from 206 countries will compete in 306 events over 42 sports, with a global audience of billions set to tune in for the 31st Olympiad in Brazil's second-biggest city.

Rio will light the Olympic flame at Maracana Stadium after a buildup that has seen Brazil fall from emerging powerhouse to financial hardship since it was awarded the games seven years ago.