An online petition with more than 350,000 signatures calling for the Tokyo 2020 Games to be cancelled has been submitted to organisers on Friday.
The campaign, called "Stop Tokyo Olympics", claims holding the Games will divert crucial medical services from the general public.
It comes as coronavirus cases continue to rise in Japan, where less than two per cent of the population has been vaccinated.
Tokyo 2020 president Seiko Hashimoto says she is taking opinions against the Olympics "seriously" and hopes details of the medical plans in place will help reassure the public of a "safe and secure" Games.
On Friday, the Japanese government expanded a state of emergency, due to last until the end of the month, to a total of nine areas to try and slow the rate of infections.
The additions include Japan's northern island state of Hokkaido, where the Olympic marathon will be held, as well as Hiroshima and Okayama in western Japan.
Around 40 Japanese towns have also recently abandoned plans to host Olympic athletes for training camps and cultural exchanges before the Games begin - the latest signal of unease among people in Japan over hosting the event in the midst of a global pandemic.
Coe confident vaccines will allow Olympics to go ahead
World Athletics president Sebastian Coe said on Friday he is confident the Tokyo Olympics will go ahead as planned this year with Covid-19 vaccines giving athletes greater access to training and competitions in the build-up.
The Olympics were postponed in March last year following the start of the pandemic but Coe said he believes athletes are in a different frame of mind heading into the July 23-August 8 Games.
"Firstly, there's the vaccine and we were a long way away from even thinking about that at this stage last year," Coe told Reuters.
"I know at this stage (last year) athletes were beginning to find it really difficult to maintain their training regimes and competitions were beginning to slide off the radar screen. Now they're having greater access to training and competitions.
"I can understand bystanders looking at this and being fearful - but that just reinforces for us the need to make sure people do understand sport actually is good at this.
"I want to reassure the Japanese people that we take this seriously, with a rigorous focus on the COVID protocols. We've staged events with crowds in many places in the world... done it successfully and haven't produced a great spike in numbers.
"We recognise sport does play a really important part in our communities. There are billions of people across the globe that want the Games to take place, the athletes and broadcasters want the Games to take place."
Coe said the Games would have a different feel with fans not allowed in from abroad, while a decision on Japanese-based spectators has yet to be made.
"Everybody wants stadiums full of noisy, passionate people - but if the Games have to take place without crowds, or certainly with fewer people in stadiums, the athletes, the world of sport, accepts that now," Coe added.