Tokyo CNN  — 

Thousands of volunteers have pulled out of the Tokyo 2020 Olympics in recent weeks, organizers said, fueling concerns Japan may not be ready to host the rescheduled Games as the country struggles to rein in a new wave of Covid-19 cases.

About 10,000 of the 80,000 registered volunteers supporting athletic events had quit as of Wednesday, according to Tokyo 2020 Organizing Committee officials.

Toshiro Muto, chief executive of the Organizing Committee, told Japanese media he does not believe the volunteer withdrawals will impact the operation of the Games, which were postponed last year due to the pandemic. The rescheduled event is due to start on July 23.

Volunteers are an instrumental part of the Summer Olympics. They help staff operate Olympic facilities and venues, and assist spectators and athletes. So if more continue to drop out, it could pose additional difficulties for organizers.

However, no foreign spectators are allowed into Japan for the Games, so organizers may not need as many volunteers as other host cities have in years past.

Work continuing on the Ariake Urban Sports Park, one of the venues for the Tokyo Olympics, on Tuesday.

A first cohort of volunteers dropped out in February – the same month the president of the Games’ organizing committee resigned. The official, Yoshiro Mori, stepped down after sexist remarks he made in a meeting were leaked.

Though officials did not say why most of the 10,000 volunteers quit, it is likely tied to the pandemic. Opinion polls show most of the Japanese public oppose holding the Olympics, with hospitals overwhelmed by a fourth wave of Covid-19 cases and the vast majority of people still unvaccinated.

The country has reported more than 752,000 total coronavirus cases and more than 13,200 deaths, according to Johns Hopkins University. Daily new cases have been in the low thousands in recent days, declining from a fourth-wave peak of nearly 8,000 on April 29.

Japan’s vaccine rollout has also gone much slower than expected. While there is enough supply to vaccinate much of the country’s 126 million people, there is a bottleneck of medical professionals available to administer them. Only nurses, doctors and dentists can legally give vaccines.

Staff prepare Moderna coronavirus vaccines for use at a newly opened mass vaccination centre in Tokyo on May 24.

Currently, just the elderly and medical professionals are eligible to receive a vaccine. Muto, the CEO of the Olympic Organizing Committee, said doses of the Pfizer-BioNTech vaccine will be provided to Olympic athletes, but not to volunteers, who are being asked to use public transportation to commute to the Games. Olympic Minister Tamayo Marukawa said the IOC would give Japan 20,000 vaccines, but negotiations for who receives those doses are ongoing.

Last week, the editorial board for one of the country’s leading newspapers, Asahi Shimbun, accused Prime Minister Yoshihide Suga of holding the Olympics “against the will of the public” and called for the event to be canceled.

Meanwhile, a group of United States public health experts warned that pushing ahead with the Olympics as planned could put athletes and the public at risk. They said Japanese authorities and Tokyo 2020 organizers needed to reconsider their approach to risk management and recognize the limits of measures like temperature screening.

“We believe the IOC’s determination to proceed with the Olympic Games is not informed by the best scientific evidence,” the authors wrote in the New England Journal of Medicine. “For us to connect safely, we believe urgent action is needed for these Olympic Games to proceed.”

A handful of prominent business leaders have also voiced concerns about the event. Last month, the CEO of e-commerce giant Rakuten, Hiroshi Mikitani, told CNN it would be a “suicide mission” for Japan to host the games.

Also in May, the Tokyo Medical Practitioners Association, an organization of about 6,000 doctors in the capital, wrote a letter calling for the Games to be scrapped.

Japanese authorities recently extended a state of emergency for much of the country, including Tokyo, until June 20 – about a month before the Olympics are set to begin.

US citizens were warned against traveling to Japan last month due to the spike in Covid-19 infections.

Staff prepare Moderna coronavirus vaccines for use at a newly opened mass vaccination centre in Tokyo on May 24.

Olympic organizers have maintained they’re confident the Olympics can be held safely and securely. Canceling the Olympics would also be costly for both Japan and the International Olympic Committee (IOC), especially due to the loss of broadcasting revenues.

Several officials have said it would be impossible to postpone the Games a second time.

“All the stadiums are booked for other events already. It has been such hard work to postpone by one year … it is impossible to postpone it again,” Tokyo 2020 President Seiko Hashimoto told Nikkan Sports, a Japanese newspaper, in an interview published Thursday.

Dick Pound, the longest-serving IOC member, told CNN this week that “none of the folks involved in the planning and the execution of the Games is considering a cancellation.”

“That’s essentially off the table,” he said.

CNN’s Emiko Jozuka, Junko Ogura and Blake Essig contributed to this report.