The head of a Japanese doctors union on Thursday warned holding the Olympic Games in Tokyo this summer, with tens of thousands of people gathering from around the world, could lead to the development of a new "Olympic" strain of the coronavirus.

Although Japan has repeatedly pledged to hold a "safe and secure" 2020 Olympics in Tokyo after a year-long postponement, it is struggling to contain a fourth wave of the pandemic and preparing to extend a state of emergency that covers much of the country.

Japanese officials, Olympics organisers and the International Olympic Committee (IOC) have all vowed the Games will go ahead, albeit under strict virus prevention measures. Foreign spectators have already been banned and a decision on domestic viewers is expected next month.

But even with these steps in place, worries remain about the influx of athletes and officials into Japan, where the vaccine process remains glacially slow and just over 5 per cent of the population have received inoculations.

With people from over 200 nations and territories set to arrive in Tokyo, it will be dangerous to host the Games in July, said Naoto Ueyama, head of the Japan Doctors Union.

"All of the different mutant strains of the virus which exist in different places will be concentrated and gathering here in Tokyo. We cannot deny the possibility of even a new strain of the virus potentially emerging after the Olympics," he told a news conference.

"If such a situation were to arise, it could even mean a Tokyo Olympic strain of the virus being named in this way, which would be a huge tragedy and something which would be the target of criticism even for 100 years."

Poll after poll has shown the majority of the public is opposed to tens of thousands of athletes and officials descending on a country that has mostly remained closed to foreigners since last year and where vaccinations have proceeded slowly.

On Wednesday Tokyo 2020 chief executive Toshiro Muto attempted to reassure those concerned, insisting “things are properly being managed”.

“There has been some feedback pertaining to a potential cancellation or postponement but nobody has explicitly mentioned a view that we should cancel or postpone the Games,” he said.

“Rather the board members mentioned that Tokyo 2020 has made an effort to come this far. Things are properly being managed.

“We as board members understand that we need to communicate that to Japanese people in the general public. We need to be more mindful in how we can communicate what you are doing to (those) outside Tokyo 2020.”

Telegraph Sport disclosed on Friday how the UK Government has assured British athletes they will get both jabs in time after taking advantage of the special deal struck between the Olympics and Pfizer-BioNTech.