Thousands flocked to London's Olympic Park on Friday for the spectacular opening ceremony heralding the start of the 2012 Games.

Seven years of planning were culminating in a breathtaking £27m show devised by Slumdog Millionaire director Danny Boyle.

At the end of the three-hour ceremony, the Queen will declare open the Games of London and the Olympic cauldron will be lit.

The ceremony comes at the end of a day that has seen the Olympic torch complete its 70-day odyssey around the British Isles.

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Bells also rang out across the UK as the final countdown to the start of the 2012 Olympics began.

Big Ben was joined by hundreds of churches across the nation as it chimed non-stop for three minutes to ring in the Games.

The Prime Minister said the country would show the world "the best of Britain" over the next two weeks after describing previews of tonight's £27m opening ceremony as "spine-tingling".

David Cameron pledged Britain was ready to welcome the "greatest show on earth" after US presidential hopeful Mitt Romney cast doubt upon the country's readiness yesterday.

Jacques Rogge, president of the International Olympic Committee (IOC) added: "London is ready."

The Queen, who was following in the footsteps of her great-grandfather and father by opening the third London Olympiad, spoke earlier of the growing excitement as the torch went around the UK.

She told heads of state and VIPs at a reception: "To me the spirit of togetherness is a most important part of the Olympic ideal, and the British people can be proud of the part they have played in keeping the spirit alive.

"Many sports played in these Games have their historic roots in this country; and as a nation we have an abiding passion for sport, as well as a tradition of fair play and a good-natured sense of fun."

US First Lady Michelle Obama, who is leading the US presidential delegation which includes a ringside seat at tonight's ceremony, was also in east London to give her own personal good luck message to Team USA.

Mrs Obama urged America's athletes to "have fun, breathe a bit, but also win", as she met them at their training base.

Oscar-winning director Boyle said the curtain-raiser at the Olympic Stadium was fitting both for London and everyone who will compete at the Games.

Special effects, big names and bags of enthusiasm will be used to help celebrate the best of British in Stratford, east London.

Millions more globally are expected to tune in on television but many competitors will be missing from the long and late-starting athletes' parade.

Competition clashes or just preferring to rest instead as part of vital preparations mean that British swimmers, athletes, track cyclists and rowers will skip the ceremony.

Team GB has previously estimated about half of the 541-strong team will not attend, meaning major stars such as Jessica Ennis, Victoria Pendleton and Mo Farah may not parade at the climax of the big budget extravaganza.

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  • London Olympic Games - Royal Welcoming Ceremony

    The Duchess of Cambridge with the President of Mongolia Elbegdorj Tsakhia (left) and Erdene Elbegdorj at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    Queen Elizabeth II meets US First Lady Michelle Obama and US Ambassador Louis Susman at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    Prime Minister David Cameron chats with Prime Minister of Jamaica Portia Simpson Miller and St Lucia Prime Minister Kenny Anthony at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    Prime Minister David Cameron chats with Russian Prime Minister Dimitri Medvedev at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    Prime Minister David Cameron chats with Prime Minister of Jamaica Portia Simpson Miller and St Lucia Prime Minister Kenny Anthony at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    UK Foreign Secretary William Hague chats with guests at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    Princess Beatrice (left) speaks to guests at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    Prince Harry meets with the President of Gabon Ali Bongo Ondimba and his wife Sylvia at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    Princess Beatrice (right) speaks to the Prime Minister of Kyrgyzstan Omurbek Babanov (left) and Rita Birbaeva at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    US First Lady Michelle Obama and US Ambassador Louis Susman (left) meet the Duchess of Cambridge at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    US First Lady Michelle Obama (right) speaks to guests at a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • London Olympic Games - Royal Welcoming Ceremony

    US First Lady Michelle Obama and US Ambassador Louis Susman attending a reception at Buckingham Palace, London, to welcome Heads of State and Heads of Government to the UK before they travel to the Olympic Stadium for the Opening Ceremony of the London 2012 Olympic Games.

  • Reception At Buckingham Palace For Heads Of State And Government Attending The Opening Ceremony Of The Olympics

    LONDON, ENGLAND - JULY 27: Prime Minister of St Luica Kenny Davis Anthony arrives for a reception at Buckingham Palace for Heads of State and Government attending the Olympics Opening Ceremony at Buckingham Palace on July 27, 2012 in London, England. (Photo by Chris Jackson/Getty Images)

  • Reception At Buckingham Palace For Heads Of State And Government Attending The Opening Ceremony Of The Olympics

    LONDON, ENGLAND - JULY 27: President Ilham Aliyev of Azerbaijan and First Lady Mehriban Aliyeva arrives for a reception at Buckingham Palace for Heads of State and Government attending the Olympics Opening Ceremony at Buckingham Palace on July 27, 2012 in London, England. (Photo by Chris Jackson/Getty Images)

  • Reception At Buckingham Palace For Heads Of State And Government Attending The Opening Ceremony Of The Olympics

    LONDON, ENGLAND - JULY 27: Deputy Prime Minister Nick Clegg and his wife Miriam Gonzalez Durantez arrive for a reception at Buckingham Palace for Heads of State and Government attending the Olympics Opening Ceremony at Buckingham Palace on July 27, 2012 in London, England. (Photo by Chris Jackson/Getty Images)

  • Reception At Buckingham Palace For Heads Of State And Government Attending The Opening Ceremony Of The Olympics

    LONDON, ENGLAND - JULY 27: Miriam Gonzalez arrives for a reception at Buckingham Palace for Heads of State and Government attending the Olympics Opening Ceremony at Buckingham Palace on July 27, 2012 in London, England. (Photo by Chris Jackson/Getty Images)