The traditional ceremony to light the Olympic flame takes place at the ancient site of Olympia in Greece on Thursday, signalling the final countdown to the start of the Games in London.
An actress playing a high priestess will light the flame using the direct rays of the sun, in a solemn occasion attended by the president of the International Olympic Committee, Jacques Rogge, as well London organising committee chief Sebastian Coe.
Greek President Carolos Papoulias is also expected to attendt the function, despite the debt-crippled country in political paralysis after Sunday's parliamentary elections, which saw parties hostile to austerity measures gain ground.
After giving thanks to the god Apollo, "king of the sun and the idea of light", the flame will be handed over to the first relay runner, Greece's open water swimming champion Spyros Gianniotis.
He will then pass it to 19-year-old British boxer Alexander Loukos, who is of Greek descent, and who got himself switched to sitting at a desk at the electricians where he is an apprentice so he didn't pick up an injury.
Gianniotis said after the full rehearsal in the ruins of the Temple of Hera on Wednesday that the torch ceremony was "a very big moment" for him, adding: "It is very moving.
"I am trembling from the emotions. It is the highest honour for an athlete to do this."
The ceremony marks the start of a week-long torch relay, which will take it to five major Greek archaeological sites, including the Acropolis, before it arrives at the old Olympic stadium in Athens, site of the first modern Games in 1896.
A British delegation will receive the flame at a night-time ceremony on May 17.
The last flame-bearers in Greece will be the weight-lifter Pyrros Dimas and the Chinese gymnast Li Ning, who lit the cauldron at the last Olympics in Beijing in 2008.
The London Olympic Games torch will tour the United Kingdom and also visit the Republic of Ireland before it arrives at the Olympic Stadium in east London on July 27 to a worldwide television audience of billions.
The torch's route in Britain starts on May 19 at Land's End, the southernmost tip of England to begin an 8,000-mile (12,875-kilometre) journey.
From June 3-7, it will visit Northern Ireland and then the Republic of Ireland -- the only country outside the United Kingdom on the torch route.
The inclusion of the Republic of Ireland would have been unthinkable just a few years ago and shows the ever-closer ties between it and Northern Ireland, 14 years after a peace agreement largely ended three decades of sectarian strike in the north.
In mainland Britain, a soldier wounded in Afghanistan and a 100-year-old woman are among 7,300 people who will carry the torch, organisers have said.
Also among the torchbearers is Jim Redmond, the father of former British 400 metres runner Derek Redmond, who famously helped his injured son hobble across the line during the 1992 Barcelona Olympics.
The torch relay culminates on July 27 with the final leg from Hampton Court palace, the riverside former home of King Henry VIII, to the Olympic Stadium in east London for the opening ceremony that day.
Coverage of the torch lighting ceremony will be transmitted for the first time live on the Internet.
The torch is a reminder of the ancient Olympics, when a flame burned throughout the Games. The tradition was revived in 1936 for the Olympics in Berlin.
No overseas legs of the torch relay have been planned this time round after those before the Beijing Games were hit by widespread protests against China.