A nine-year-old girl has officially opened the the 2012 Olympics stadium, at a ceremony in east London.
Niamh Clarke-Willis joined Locog head Lord Coe to hit a button which launched balloons into the sky above the venue for this summer's Games.
Around 40,000 members of the public were at the Olympic Stadium in Stratford to witness the opening, which included a laser light show.
The "2,012 hours to go" event tested the park's management and security.
Lord Coe said: "It's a fantastic feeling. The seven years have just flown by. Tonight is only the start of the story.
"We want thousands of young people to be inspired to take up sport. We hope that for a few of them it will be the start of their journey.
"I'm grateful to everyone who came here tonight to celebrate this moment in history."
Spectators had to queue to enter the venue after airport-style security checks.'Insufficient clothing'
Simon Levy, who came to the Olympic Park for the first time on Saturday, said: "It's not a problem, really. It's much quicker than the airport and it's good to be checked because now we know we're safe."
Police helicopters flew over the park and armed police patrolled the area.
Adrian Casy, a security guard at the Olympic Stadium, said Saturday's events were among the main rehearsals for the games, particularly in moving and managing the crowds of spectators from the park and from one venue to another.
"Honestly, so far, so good, although we're still trying hard to make it run smoother," said Mr Casy, adding that some spectators were wearing "insufficient clothing" to cope with the weather conditions.Spinning targets
Organisers Locog said young people aged eight to 14 were asked to register for the opportunity to open the stadium during a series of sporting events held at the venue.
The first 100 youngsters who applied were picked to go through to the final round.
Paralympic gold medal-winning archer Danielle Brrown will shoot arrows at a series of spinning targets to select one young person from the audience to open the stadium.
Some 140,000 people are expected at the Olympic site over six days.
The celebrations are part of the British Universities and Colleges Sport Outdoor Athletics Championships and the Visa London Disability Grand Prix which are test events for the venue.
London 2012 hopefuls Perri Shakes-Drayton and Holly Bleasdale are competing at the BUCS event which runs from 4-7 May.
TV presenters Vernon Kay and Gabby Logan hosted the event which saw entertainment from impressionist Jon Culshaw, actor Hugh Bonneville, singer and former Spice Girl Melanie C, rapper Chipmunk and comedian Jack Whitehall.
Later in the week, the Olympic Stadium will also play host to the Sainsbury's 2012 School Games, for 1,600 school-aged elite athletes.