More than 40,000 spectators watched as a cascade of white balloons was released to open London's Olympic stadium on Saturday, May 5 exactly 2,012 hours before the Games begin, AFP reported.

Capping off an evening of music, comedy and fun sports events, Paralympic gold medal-winning archer Danielle Brown shot arrows at spinning targets to select the name of a youngster in the audience to open the east London stadium.

A dazed-looking Niamh Clarke-Willis, 9, joined Sebastian Coe, the chairman of Games organisers LOCOG, in pressing a large button to release the balloons into the chilly night sky over the stadium.

The 80,000-capacity venue hosts the Olympic opening ceremony on July 27.

Saturday's event, named "2012 Hours to Go: An Evening of Athletics and Entertainment", allowed organisers to test the Olympic Park's airport-style security checks.

It was also a major test of London's transport system ahead of the Games as the Underground train network's Jubilee line, which serves the stadium, was further crammed with football fans leaving the FA Cup final in north London.

The crowds at the stadium watched as Olympic rowing champion Steve Redgrave and "Downton Abbey" actor Hugh Bonneville joined other celebrities and sport stars in a series of fun contests to test out the running track.

Former Spice Girl Melanie C and comedian Jack Whitehall performed, while the Military Wives, a group of British soldiers' wives whose charity single topped the charts last Christmas, led a rendition of the national anthem.

Earlier, students had tested out the stadium as part of the British Universities and Colleges Sport championships.