The Olympic flame will begin its six-week worldwide odyssey in Sydney on Friday, the first stage of a long journey that ends at the August 13 opening ceremony in Athens.

Sydney 400 metres champion Cathy Freeman will run the opening leg of the relay, which will travel to 33 cities in 34 days and take the torch to all six continents for the first time.

Celebrities from US movie star Angelina Jolie to Japanese pop singer Yukio Hashi will join the 3,600 torchbearers.

An estimated $US45 million ($A63 million) will be spent on taking the skittle-shaped torch, inspired by an olive leaf, around the world on its own private jumbo jet dubbed Zeus.

Aviation authorities had to issue a special permit to allow the gas-fired torch to keep burning while it is flying.

It will ride the skies in a special lantern with a team of attendants making sure the sacred light of Apollo is not extinguished by accident.

The chrome and olive wood torches can burn for up to 15 hours.

Far from the lone runner of popular imagination, the torch procession will resemble a US presidential motorcade as each bearer is flanked by escort runners and a fleet of 15 backup vehicles.

Previous torch processions at Sydney and Atlanta were largely domestic affairs with a brief international leg.

This time the flame is set to make its debut in Africa and Latin America, with stops at Cape Town in South Africa and Rio de Janeiro in Brazil.

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