Japan's Emperor Naruhito on Thursday acknowledged the challenges of staging the Tokyo Olympics during a pandemic, telling IOC chief Thomas Bach it was "a far from easy task", local media said.

International Olympic Committee chief Bach paid a courtesy visit to the imperial palace a day before the opening ceremony at which the emperor is expected to announce the start of the Games.

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"The managing of the games, while at the same time taking all possible measures against Covid-19, is a far from easy task," the emperor told Bach in English, according to Kyodo News agency.

"I would like to pay tribute to all those who have been involved in the management of the games for their efforts at various venues," he said.

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The 61-year-old emperor will be at Friday's ceremony along with only around 950 dignitaries and officials because of strict virus rules barring fans.

His wife, Empress Masako, will not take part in the ceremony.

Tokyo is seeing a surge of virus cases driven by the Delta variant, registering 1,979 infections on Thursday, the highest figure since a winter wave.

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Last month, Prime Minister Yoshihide Suga was forced to dismiss claims that Naruhito was "concerned" the Olympics could spread Covid-19.

Naruhito is expected to declare the Games open but reportedly may avoid using the word "celebrate" given the environment of the pandemic.

The emperor, who took the throne in 2019, is the honorary patron of the Tokyo Olympics.

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Imperial family members are not expected to attend any other Olympic events, which will take place almost entirely behind closed doors to limit infections.

Naruhito's father, then Emperor Akihito, proclaimed the start of the 1998 Nagano Winter Games, while his grandfather, then Emperor Hirohito, declared the opening of both the 1964 Tokyo Summer Games and the 1972 Sapporo Winter Games.