Doubts have persisted over the Games in the build-up to the event, which was postponed last year due to the COVID-19 pandemic.

Variants and a rise in cases in Japan have led to speculation over whether the Games can be held as planned.

Hamada told Japan’s Mainichi newspaper that organisers would need to secure medical personnel for the event, without jeopardising treatment of COVID-19 patients and the vaccination effort in the host nation.

"The question is if we can allocate medical resources to hold the Olympics while handling those priorities," Hamada told Mainichi.

"If that is difficult, we have no choice but to cancel the Olympics."

Tokyo 2020 has faced criticism online and from medical personnel following a request to secure 500 nurses for the Games.

Around 10,000 medical workers are expected to support the Games.

Tokyo 2020 chief executive Toshiro Muto insisted last week that the main condition of the Tokyo 2020 request was that it "must not negatively affect regional medical care."

Hamada has suggested vaccination of athletes and officials prior to Tokyo 2020 could reduce the potential workload on medical personnel.

The professor suggested holding the Games without spectators could also reduce the risk of COVID-19 spreading.

"Recent studies have shown that vaccinations are effective in preventing infections, as in Israel, where most of the population has been vaccinated twice," he told Mainichi.

"It is better to vaccinate athletes coming from overseas as much as possible.

"This will reduce the probability of mutant strains being carried into Japan, which will help lighten the burden on the medical field.

"If we allowed spectators, the risk of clusters of infections occurring at competition sites or in the city would increase.

"At this point, no one can predict the state of infections in July, so it is better to take measures based on the assumption that there will be no spectators."

The International Olympic Committee (IOC) today announced developers of the Pfizer COVID-19 vaccine are set to donate doses to athletes heading to the Games.

National Olympic Committees will be tasked with coordinating distribution with their respective Governments "in accordance with each country’s vaccination guidelines and consistent with local regulations".

The Chinese Olympic Committee has also offered to vaccinate Tokyo 2020 and Beijing 2022 teams, with the IOC paying for the cost of each dose.

They will only be available in territories which have approved the Chinese vaccines for use, which will also be the case as part of the IOC's deal with Pfizer.

The signing of the deal comes after organisers released the updated version of their "playbooks", which outline the strict rules participants must adhere to at the Games.

Athletes and all those with close proximity to competitors will be tested daily and everyone at the Games will be required to take two COVID-19 tests within 96 hours before they fly to Japan.

Visits to restaurants and bars have been banned, while athletes have been told to arrive no earlier than five days before their event and depart no later than two days after to limit the number of people at the Athletes' Village.

The IOC has warned those who breach the rules could be stripped of their accreditation, and the regulations will be in place irrespective of whether participants have been vaccinated or not.

Tokyo 2020 President Seiko Hashimoto has acknowledged the Olympic and Paralympic Games may be held behind closed doors.

A decision on spectator limits at the Games will not be taken until June.

The decision would come a month prior to the planned July 23 Opening Ceremony of the Olympic Games.