The Olympic Games' torch is kindled by the sun's rays at the site of ancient Olympia, starting the countdown to this summer's London games.
The ceremonial lighting sparks a relay that will continue until the same flame lights the Olympic stadium's cauldron during the opening ceremonies on July 27.
The relay's first torchbearer, Spyros Gianniotis, a Greek swimmer who won the gold medal in the 10km open water event in the 2011 world championships, started the seven-day leg of the relay through Greece.
The flame will be delivered to the London organisers on May 17 and flown to Britain a day later.
Several thousand spectators also watched the ceremony from the grassy slopes hugging the ancient sports arena.
The British leg of the relay will travel 12,800 km around the country before finishing inside the Olympic stadium.
London, also the host of the 1948 games, will be the only city ever to twice receive the Olympic flame.
Sarah Sheffer, Reuters
