Bells pealed out across Britain and the Olympic flame travelled down the River Thames in the sumptuous royal barge, as London made its final countdown to the opening ceremony.
The Olympic torch was rowed on Friday along the Thames onboard the Gloriana, Queen Elizabeth II's vast red and gold barge, on the last day of its 10-week, 12,800-kilometre relay around Britain and Ireland.
The flame's epic journey, which began in Greece on May 10, ends at what is promised to be a spectacular opening ceremony in the Olympic Stadium in Stratford in east London.
A fly-past by the famous Red Arrows formation jets and the striking of the world's biggest tuned bell are expected to start the extravaganza masterminded by Oscar-winning film director Danny Boyle at 8:12pm, or 2012 (1912 GMT).
About 80,000 spectators and VIPs, including about 80 world leaders and US First Lady Michelle Obama, packed Olympic Stadium for the show, which will feature the traditional athletes' march and the Queen lighting the cauldron.
Other elements of the three-and-a-half-hour showpiece have remained under wraps but soccer icon David Beckham will feature, plus James Bond and ex-Beatle Sir Paul McCartney -- and even Britain's National Health Service.
Spectators will be urged to join in sing-a-longs and help create spectacular visual scenes at an event that sets the tone for the sporting extravaganza, when 16,000 athletes from 204 countries share the thrill of victory and despair of defeat with 11 million visitors.
$14 billion question
The opening ceremony, costing $42 million and watched by more than one billion TV viewers worldwide, kicks off a two-week festival of sport.
The Games will also answer the question on Britons' lips: Were seven years of planning, construction and disruptions, and a price tag of $14 billion during one of the country's worst recessions, actually worth it?
It follows China's jaw-dropping curtain-raiser to the Beijing 2008 Games, when thousands of drummers, dancers and deafening pyrotechnics received wide acclaim -- and ramped up expectations for the British show.
Excitement in Britain, which has built up to the Olympics with a nationwide torch relay, was at fever-pitch ahead of the ceremony with Union Flags visible in gardens, windows and streaming from cars.
Millions of Britons packed pubs and gathered with friends and relatives for the grand opening of the greatest show sports on earth, while thousands of excited fans gathered at big screens at London's Hyde Park and other outdoor locations across the capital.
"This is a very, very tense moment but so far I'm cautiously optimistic," said Boris Johnson, mayor of London, the only city to host the Summer Games three times.
"I'm just worried that I haven't got enough to worry about at the moment," added the mayor, known for his witty asides.
Counter-terrorism chiefs have played down fears of a major attack on the Games, and British Prime Minister David Cameron said that a safe and secure Olympics was his priority.
"This is the biggest security operation in our peacetime history, bar none, and we are leaving nothing to chance."
A series of doping scandals have tarnished the Games' image in the buildup, with at least 11 athletes banned so far, and Greek triple jumper Paraskevi Papachristou became the Olympics' first "twitter victim" when she was withdrawn from the team over tweeted comments deemed racist.