Bells pealed out across Britain on Friday 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 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 (8,000-mile) 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.
Prime Minister David Cameron urged the country to make the most of its time in the global spotlight.
"Britain is ready to welcome the greatest show on earth," he told reporters.
"We have got a great past, a very exciting future and this is a great moment for our country. We must seize it."
Thousands of VIPs including over 100 world leaders gathered in the British capital for the ceremony, with guests ranging from Russian premier Dmitry Medvedev to US First Lady Michelle Obama and Hollywood star Angelina Jolie.
More than a billion people are expected to tune in worldwide to watch the show devised by British film director Danny Boyle.
No Olympics ceremony is complete without a flame, and four-time Olympic gold rowing medallist Matthew Pinsent took it from Hampton Court Palace and lit a cauldron onboard the Gloriana.
Powered by 16 oarsmen, the barge which carried the queen during her 1,000-boat diamond jubilee river pageant last month, sailed east towards the Olympic Stadium, flanked by some 90 other boats.
It stopped at the giant Olympic rings hung under Tower Bridge and was taken to City Hall, the headquarters of London mayor Boris Johnson, where it was to stay until the ceremony.
Organisers did not reveal how the torch would arrive at the stadium.
In Westminster, Big Ben chimed for three minutes from 8:12 am (0712 GMT) to ring in the Olympics, 12 hours ahead of pre-ceremony entertainment scheduled to start at the symbolic time of 20:12.
The huge bell at the British parliament was joined by hundreds of bell-ringers across Britain -- including one onboard the Gloriana -- in a national cacophony to mark the start of the Games.
Culture minister Jeremy Hunt's enthusiastic attempt to take part in the mass ringing caused an Internet sensation when his bell flung off its handle into a group of women behind him.
Meanwhile, there was fierce speculation over the mystery VIP who will light the Olympic cauldron at the stadium.
Organisers have kept the final torchbearer's identity a secret, but favourites include five-time Olympic rowing gold medallist Steve Redgrave and Roger Bannister, the first man to run a mile in under four minutes.
David Beckham has reavealed that he features in the opening ceremony.
The former England captain, who played a key part in London's bid seven years ago but was omitted from the British football team for the Olympics, said the thought of the ceremony gave him "goosebumps".
"I have been lucky enough to have been involved in some amazing sporting moments in my career, but nothing can compare with what is about to take place in London," Beckham wrote in The Sun newspaper.
Sneak previews of the 27 million pounds ($42 million, 35 million euros) opening ceremony suggest it will be a grand but eccentric production, reflecting Boyle's philosophy.
The "Slumdog Millionaire" Oscar winner has promised to create a "picture of us as a nation" and revealed that the show will feature live farm animals and includes a tribute to the National Health Service.
"It's been a long road and we're almost there," Boyle said Friday.
The Games are guarded by Britain's biggest ever peacetime security operation backed by a force of more than 40,000 military and civilian personnel.