Tokyo Olympics: Star Japanese athletes Naomi Osaka, Kei Nishikori raise concerns over Games

Japan's Kei Nishikori has expressed concerns about staging the Olympic Games in Tokyo this summer, as Japan battles to contain a surge in COVID-19 cases.

Fellow tennis player Naomi Osaka has raised similar concerns, saying that the risks of holding the Games amid the pandemic should continue to be carefully discussed.

Both are figureheads for Japan's Games promotion, as two of the country's most well known athletes.

Japan has extended a state of emergency in Tokyo and three other areas until the end of May, raising more questions about whether the Games should go ahead. Its vaccination rate is also the lowest among wealthy nations.

"This is not like 100 people like these tournaments," Nishikori said at the Italian Open in Rome on Tuesday (NZ time).

"It's 10,000 people in a Village, playing a tournament. I don't think it's easy, especially (with) what's happening right now in Japan, it's not doing good."

The Tokyo Olympics were already postponed from 2020 and opposition seems to be rising in Japan about holding the Games this year. 

World No.2 Osaka said rising COVID-19 levels in Tokyo were concerning and she was not sure the Games should go ahead.

"Of course I would say I want the Olympics to happen because I'm an athlete and that's sort of what I've been waiting for my entire life," Osaka said on Monday.

"But I think that there’s so much important stuff going on, and especially the past year."

Nishikori, who won bronze in the men's singles at the 2016 Olympics in Rio, added that there was still time before a decision had to be made but was wary about the potential for an outbreak in the Athletes Village.

"You can make a good bubble and maybe you can do it," he said.

"There is some risk too. What happens if there's 100 cases in the Village? Or it can be thousands."

The 2020 Olympics were postponed by a year due to the pandemic and organisers have stood firm in saying that the global sporting showpiece would go ahead this summer.

Several test events with foreign athletes have been successfully held, but a visit by International Olympic Committee head Thomas Bach - scheduled for May 17 - has been cancelled.