London is welcoming around 10,000 athletes, hundreds of thousands of visitors and a worldwide television audience for the formal opening of the Olympic Games Friday.

Organizers have dealt with a series of last-minute problems, including scrambling to deploy enough security personnel, after a private contractor reported problems putting together a large enough force.

Britain's Queen Elizabeth will officially open the games. The competition in 26 sports runs until August 12.

The extravagant opening ceremony Friday night will be directed by Danny Boyle, the director of the Oscar-winning movie “Slumdog Millionaire”. The parade of athletes will start with Greece and end with Britain.

On the eve of the opening, British Prime Minister David Cameron said his biggest concern is a “safe and secure” Olympics.

About 36,000 troops, police and hired contractors will guard the Olympic venues and the streets of London and other British cities. After the private security firm G4S acknowledged earlier this month that it would not be able to secure all of the 10,000 contractors it had agreed to provide, British officials called up additional service members to fill the gap.