PHOTOS: Sun god Apollo presides over final Olympic flame rehearsal

The high priestess raised her arms towards the sky, invoking the sun god Apollo at the birthplace of the ancient Olympics on Wednesday in the final rehearsal for the flame that will burn at the Rio Games later this year.

In a long pleated robe she then knelt solemnly to the ground and lit the torch within a few seconds using a concave mirror to catch the sun's rays.

Hundreds of onlookers stood quietly near the ruins of the Doric temple to the goddess Hera at the site of the first modern Games, held in 1896 at Ancient Olympia in southern Greece. The ritual with the high priestess and the torch was established eight decades ago for the Berlin Games.

The flame will be used as a back-up if overcast skies loom over the official ceremony on Thursday, but weather forecasts predict that event will be similarly blessed by abundant sunshine.

"It's very special. It's been a dream of mine to come here for many, many years," said Mark Ledeux, a British tourist, standing on the grassy slopes of the stadium where Greeks competed in the ancient games.

From past games Ledeux has amassed a collection of about a dozen torches. They can be bought at various sites as memorabilia.

During the rehearsal a dozen young women in long, pleated robes, escorted by a dozen male youths, danced to the rhythm of a drum and the sound of a flute, according to ancient Greek tradition.

The rehearsal ended with the high priestess, played by actress Katerina Lehou, handing the flame and an olive branch to a volunteer filling in for the first torchbearer - Greek gymnast Eleftherios Petrounias, world champion on the rings in 2015.

On Thursday, Petrounias will pass the torch to Brazilian volleyball player Giovane Gavio, a two-time Olympic gold medallist in Barcelona 1992 and Athens 2004.

The torch will then begin a six-day relay across Greece, passing through the town of Marathon, which gave its name to the endurance race, as well as a camp for refugees and migrants in Athens, housing mostly Afghans and Iranians, the International Olympic Committee has said.

There, one refugee will bear the torch in the name of all refugees. As many as 10 refugees - competing as Team of Refugee Olympics Athletes (ROA) - could take part in this year's Games.

The torch will arrive in Brazil on May 3 for a 100-day relay across the country, travelling through 500 cities and villages in every Brazilian state and borne by some 12,000 torch bearers before arriving for the opening ceremony in Rio on Aug. 5 for the first Games in South America.