Three activists, according to the Greek police, two women and one man, were arrested.

The activists waved the Tibetan flag and Hong Kong's revolution flag atop the historic monument, chanting "Boycott Beijing 2022" and "Free Tibet", "just 48 hours before the Olympic Torch will be handed to Beijing in the very same place", according to a statement from the New York-based organisation Students for a Free Tibet.

The organisation is citing two arrests.

The flags that were hung up on scaffolding of the Acropolis, were confiscated by the Greek police.

Tibet has alternated over the centuries between independence and control by China, which says it "peacefully liberated" the rugged plateau in 1951 and brought infrastructure and education to the previously underdeveloped region.

But many exiled Tibetans accuse the central government of religious repression and eroding their culture.

"Now it is time for the international community, and all people of conscience, to take a stand and boycott Beijing 2022; anything less will be a clear endorsement of China's genocidal regime," Tsela Zoksang, an 18-year-old Tibetan-American, one of those detained according to Students for a Free Tibet, was quoted saying in the statement.

Hong Kong Watch, a UK-based human rights watch charity, in a statement, called on Greek authorities "to resist any pressure from the Chinese Government to extradite these activists, to release Joey Siu and the Tibetan activist Tsela Zoksang as a matter of urgency, and to allow them to return to the United States of America".

The Olympic flame will once again be lit in an empty stadium on Monday as it starts its truncated journey to Beijing for the Winter Games in February.

Like the ceremony in March 2020 to light the flame for Tokyo, and like those Games, which were put back a year, Monday's ceremony is a victim of coronavirus restrictions.

This year the rehearsal on Sunday falls on the 100th anniversary of the creation of the Executive Board of the International Olympic Committee which is holding ceremonies to celebrate.