The head of a doctors union in Japan warned Thursday that holding the Olympic Games in Tokyo this summer, with tens of thousands of people gathered 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 yearlong postponement, it is struggling to contain a fourth wave of the pandemic and preparing to extend a COVID-19 state of emergency that covers much of the country.

Japanese officials, Olympics organizers 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 audiences is expected next month.