The cost of hosting the Olympics has left only Almaty, Beijing, Oslo and possibly Lviv for the 2022 Winter Games after other cities voted no.
Director Danny Boyle has been forced to cut parts of the Olympic opening ceremony to make sure the show finishes on time.
Less than a year before London hosts the 2012 Games, scenes of rioting and looting have raised concerns about security and policing for the event.
South Africa and the United States are among at least five countries that filed initial paperwork required ahead of any potential 2020 Olympic bids.