US officials say an increase in coronavirus cases in Japan caused by variants could even be a risk to vaccinated people.
They have not banned Americans from visiting Japan, but there are worries insurance rates could be affected and that Olympic athletes may decide to no longer take part in the Games.
Many populated areas in Japan are under a state of emergency and are expected to remain so through to mid-June because of rising cases that are putting hospitals under pressure, but despite this the Games are expected to still go ahead on 23 July.
That raises concern about how the country could cope with the arrival of tens of thousands of Olympic participants if its hospitals remain overwhelmed and little of its population is vaccinated.
Japan’s chief cabinet secretary Katsunobu Kato told a regular news conference that the US warning does not prohibit essential travel and Japan believes the US support for Tokyo’s effort to hold the Olympics is unchanged.
“We believe there is no change to the US position supporting the Japanese government’s determination to achieve the Games,” Mr Kato said, adding that Washington has told Tokyo the travel warning is not related to participation of the US Olympic team.
The United States Olympic & Paralympic Committee said it still anticipates American athletes will be able to safely compete at the Tokyo Games.
Fans coming from abroad were banned from the Tokyo Olympics months ago, but athletes, families, sporting officials from around the world and other stakeholders still amount to a mass influx of international travellers.
The Japanese public in opinion surveys have expressed opposition to holding the Games out of safety concerns given that most people will not be vaccinated.
The US warning from the Atlanta-based Centres for Disease Control and Prevention said: “Because of the current situation in Japan, even fully vaccinated travellers may be at risk for getting and spreading Covid-19 variants and should avoid all travel to Japan.”
The State Department’s warning was more blunt.
“Do not travel to Japan due to Covid-19,” it said.