Thousands of people are arriving at the Olympic Park ahead of the £27m opening ceremony of the London Games.
The three-hour spectacle in the Olympic Stadium will be viewed by a global TV audience of around one billion people.
The Olympic flame is at City Hall ahead of its ceremony appearance, on the last leg of its 70-day nationwide journey.
Details of the ceremony remain a closely-guarded secret. Its artistic director, Danny Boyle, has dedicated it to the 15,000 volunteers taking part.
Mr Boyle has spoken of his “excitement” for the ceremony, as well as feeling “nervousness” for all the volunteers.
The chairman of London 2012, Lord Coe, told the BBC he was “as excited as hell”.
Crowds of people, many of them dressed up in their nation’s colours, are gathering in large numbers at the Olympic Park.
The BBC’s Claire Heald, at the Olympic Park, says transport to the stadium appears to be running smoothly and the crowds are moving quickly through security.
The day of celebration began at 08:12 BST (07:12 GMT) with a mass bell ringing. Big Ben rang for three minutes for the first time since King George VI’s funeral in 1952.
“It’s a great opportunity to show the world the best of Britain”
Says David Cameron Prime minister
In other developments:
- A fire has broken out at a pavilion in Weymouth close to where the Olympic sailing will take place. The building, due to host a VIP and media event, has been evacuated
- Lord’s cricket ground turned away spectators trying to get in to watch archery amid confusion over ticketing. The London 2012 website advertised the event’s preliminary rounds as “unticketed”, which some people interpreted as open to the public
- Ticketing delays at St James’ Park in Newcastle, which meant some fans missed a men’s football match on Thursday, were unacceptable, a senior 2012 official has said
- Three people due to work as staff at an Olympic venue in Newcastle were arrested on Wednesday on suspicion of immigration offences following accreditation checks
- Culture Secretary Jeremy Hunt narrowly avoided hitting a group of women with a bell after it flew off its handle on HMS Belfast during the co-ordinated ringing – he called the moment a “classic”
- US First Lady Michelle Obama, who is in London to lead the US delegation, told the US Olympic team at their Docklands training camp “have fun, breathe a bit, but also win”
- International Olympic Committee president Jacques Rogge praised the regeneration which has taken place in east London and said the Games would have a “tangible legacy” with, uniquely, “no white elephants”
- London taxis drivers staged a protest at Hyde Park Corner over Olympic traffic lanes
Analysis by Nicholas Witchell Royal correspondent
When Queen Elizabeth officially opens the London Olympics she will become the only head of state in the world to have opened a summer Olympiad on two occasions.
As Queen of Canada, she declared the Montreal summer games open in 1976.
The Windsors have had a long association with the Olympics. The Queen’s father, King George VI, opened the last London games, in 1948 – and the Queen’s daughter, the Princess Royal, was a member of the British equestrian team at the 1976 games in Montreal.
From Queen Elizabeth’s position as a head of state, to the glamour which attaches to the younger members of the Windsor family, the British royals have been an integral element of the British proposition which secured the 2012 Games for London.
Forecasters say the weather for the ceremony is expected to remain dry.
Prime Minister David Cameron said: “It’s a great opportunity to show the world the best of Britain, a country that’s got an incredibly rich past but also a very exciting future.
“Someone asked me yesterday what face of Britain do we want to put forward – is it Blur or the Beefeaters? – and frankly it’s both.”
‘Wave of excitement’
Mayor of London Boris Johnson told BBC Radio 5 live: “What’s so amazing is just the wave of excitement seems to pass from person to person like some benign form of contagion. Everybody is getting it.”
Tony Blair, who was prime minister when London won the Games in 2005, told the BBC: “It’s a party atmosphere but also an immense sense of national pride – of what we are and what we can show the world.”
The Olympic flame arrived at City Hall on the Queen’s rowbarge Gloriana after first weaving through the maze at Hampton Court Palace then being transported down the Thames.
The flame’s trip around the UK ends with the lighting of the cauldron during this evening’s opening ceremony, but the identity of the person who will take on the honour remains a mystery.
Europe’s largest bell will ring inside the Olympic Stadium at 21:00 at the start of the opening ceremony, said to be a quirky take on British life.
Some 15,000 sq m of staging and 12,956 props will be used, and the event will boast a million-watt PA system using more than 500 speakers.
The crowd of about 80,000 will include the Queen and a host of dignitaries and celebrities.
The Queen and Prince Philip hosted a Buckingham Palace reception for foreign dignitaries, and an opening ceremony celebration concert featuring Snow Patrol, Stereophonics, Duran Duran and Paolo Nutini is being held in Hyde Park.
*Article by BBC*
