Prime Minister Yoshihide Suga has vowed to forge ahead with preparations to hold the Tokyo Olympics, in the face of growing public opposition as Japan battles a surge in coronavirus infections.

Suga faces heightened scrutiny after Taro Kono, his administrative and reform minister, told Reuters last week the Games may not go ahead as planned, becoming the first cabinet member to voice doubt over their staging.

Kono's comments added fuel to the fire after recent media polls showed close to 80 per cent of Japanese believe the Olympics, already postponed by a year because of the pandemic, should be delayed again or cancelled entirely.

"We will press ahead with preparations, with determination of building watertight anti-infection measures and holding an event that can bring hope and courage to the world," Suga said in a policy speech at the start of a regular parliament session.

Japan has been less severely hit by the pandemic than many other advanced economies, but the recent surge in cases spurred it to close its borders to non-resident foreigners and declare a state of emergency in Tokyo and major cities.

Suga's support ratings have tumbled as critics have described the government's handling of the pandemic as too slow and inconsistent.