The three-hour spectacle in the Olympic Stadium will be viewed by a global TV audience of around one billion people.
The day of celebration began at 08:12 BST with a mass bell ringing. Big Ben rang for three minutes for the first time since King George VI’s funeral.
Lord’s cricket ground has 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 members of the public interpreted as open to the public.
But Olympic organizer LOCOG said it had not advertised or sold tickets for the ranking event and had always made it clear preliminary rounds were not open to spectators.
South Korea later claimed the first two world records of London 2012 in the men’s team and individual archery.
Meanwhile, the Olympic flame has arrived at City Hall on the Queen’s rowbarge Gloriana after first weaving through the maze at Hampton Court Palace and being carried down the Thames on the final day of the torch relay.
Around 50 boats took part in the flotilla, each reflecting London’s waterborne heritage.
The flame’s 70-day nationwide journey ends with the lighting of the cauldron during this evening’s opening ceremony but the identity of the person who will take on the honor remains a mystery.
Five-times rowing gold medallist Sir Steve Redgrave and two-times decathlon champion Daley Thompson will take part in the closing stages, although neither is expected to light the flame.
The ceremony is expected to remain dry, but weather forecasters say the jet stream is moving southwards and there will be a return to more unsettled and chillier conditions over the next few days.
There have not been any reports of major transport issues. Network Rail and the Association of Train Operating Companies said most services were running to schedule. Some roads in London were congested around the route of the Olympic torch relay, and in St. John’s Wood where the archery competition began at Lord’s cricket ground.
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.”
Mayor of London Boris Johnson said: “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.”
Danny Boyle, the artistic director of the £27 million ($43 million) opening ceremony, dedicated it to the 15,000 volunteers taking part.
“This is a live performance and it’s the actors, and in our case they’re volunteers, who have to get up there and do it.”
Europe’s largest bell will ring inside the Olympic Stadium at 21:00 BST at the start of the extravaganza, 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.
Queen Elizabeth II and Prince Philip will host a Buckingham Palace reception for heads of state and government and an opening ceremony celebration concert featuring Snow Patrol, Stereophonics, Duran Duran and Paolo Nutini will be held in Hyde Park.
More than 10,000 athletes from 204 nations will take part in the London Olympics, which has taken £9 billion ($14 billion) of public money to stage.
In other developments:
• 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 handbell after it flew off the handle on HMS Belfast during the co-ordinated ringing – he called the moment a “classic”
• American 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 staged a protest at Hyde Park Corner over Olympic traffic lanes. The protest was moved forward by three hours after police said they could not demonstrate on the Olympic Route Network from 16:00 to 03:00 BST.
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