The Olympic flame, though, did not go out. Two lamps, lit from the original flame of Olympia, accompany the relay and help light thousands of torches carried by bearers who include celebrities, politicians and athletes on its 136,794 km journey.

The Beijing torch burns on environmentally-friendly propane gas and its flame can last up to 15 minutes. Every torchbearer has a separate torch which they can buy to keep as a souvenir at the end of their run.

"(The gas) is composed of carbon and hydrogen. No material, except carbon dioxide and water remain after the burning, eliminating any risk of pollution," the Beijing Games organising committee explains on its website.

The burning system itself was designed by China Aerospace Science and Industry Corporation.

The Sydney 2000 torch used a mix of butane and propane for a rich flame effect that could also burn underwater at the Great Barrier Reef.

The 72-cm tall Beijing torch, weighing just under one kilo, is always accompanied by several vehicles and security guards on foot, while one of two portable backup lamps, follows in a van.

"The flame will often go out during the relay, due to weather conditions or problems with the gas," said former Athens 2004 Games official Pierre Kosmidis, who accompanied the flame on its long international leg four years ago.