A Japanese cabinet minister admitted Friday that "anything can happen" with the coronavirus-postponed Tokyo Olympics, becoming the first senior official to concede uncertainty about the Games as Japan and other countries battle a surge in cases.

Taro Kono, minister for administrative and regulatory reform, did not rule out the possibility of the Olympics being cancelled, with greater Tokyo and other regions currently under a state of emergency until at least 7 February.

He is the first cabinet minister to deviate from Prime Minister Yoshihide Suga's insistence that Japan is on track to hold a "safe and secure" Games, despite a state of emergency being expanded this week to cover a total of 11 regions, including Osaka and Kyoto.

"Given the coronavirus situation, anything can happen," Kono, a high-profile former foreign and defence minister, told a press briefing.

"The organising committee and the IOC must of course be thinking about back-up plans. The government is firmly preparing for the Olympics and Paralympics."

Public support for the Olympics has plummeted in Japan, with a recent poll finding that more than 80 percent of respondents think the Games should be cancelled or postponed again.

Tokyo 2020 President Yoshiro Mori said in a speech Tuesday that another postponement was "absolutely impossible", according to local media.

Mori also said Japan will decide in the coming months whether to allow foreign fans to enter for the Games, saying: "We will have to make a very difficult decision from February to March."

Suga has said Japan is committed to hosting the Games and believes the public mood will change when the country begins its vaccination programme, set for late February.

Local media quoted Olympic minister Seiko Hashimoto saying Friday that Japan is suspending an exemption that allows foreign athletes to enter the country to train while the country's state of emergency is in place.

Japanese athletes will still be able to re-enter Japan, but they will no longer be allowed to skip the 14-day quarantine period.

"We want to prioritise saving lives," Hashimoto was quoted as saying. "So as a preventative measure to eliminate risk, we want to strengthen our first line of defence a level.

"We will take the infection situation at home and abroad into account and react accordingly," she added.

The ban on non-resident foreign athletes is also likely to affect baseball and J-League football teams, who are preparing to begin their seasons.

On Thursday, Japan's Top League rugby put its season on hold just two days before it was due to begin, after a rash of players from several clubs tested positive for the virus.

The Tokyo 2020 organising committee insisted Friday that the latest anti-virus measures would help rather than hinder preparations. 

"We expect that the series of measures being implemented by the government of Japan, the Tokyo metropolitan government and other prefectural authorities will help improve the situation," it said in a statement.

"We hope that daily life can return to normal as soon as possible, and we will continue to work closely with all related parties in our preparations for holding safe and secure Games this summer."