The Summer Games are scheduled to start on July 23, after a year's delay due to the pandemic. But polls show a majority of Japanese oppose holding the event this year given warnings from health experts that it could unleash another wave of infections and spawn new, more potent variants.

Holding the Games without any spectators is a possibility and the government will decide on this next week, when it will also determine whether to lift a state of "quasi-emergency" in Tokyo and other parts of the country, Japanese Prime Minister Yoshihide Suga told reporters on Thursday.

Spectators from abroad have already been banned.

Tokyo 2020 Organising Committee officials could not be immediately reached for a comment on the Yomiuri report.

The governors of Chiba and Saitama prefectures near Tokyo have been lobbying the central government to ban spectators from night-time Olympic events in their localities.

Holding the Games without spectators would be the "least risky" option, medical experts said last month.

Government sources told Reuters on Thursday that Japan was likely to extend by two weeks or more its coronavirus containment measures in the greater Tokyo area.

Depending on the extent of the strain on the medical system, the government could reinstate a more stringent full state of emergency for Tokyo, the sources said.

Japan has not suffered the explosive COVID-19 outbreak seen elsewhere but the potential spread of more contagious variants and an initially slow vaccine rollout have fuelled concerns.

The country has recorded more than 796,800 COVID-19 cases and over 14,770 deaths. Only about 23% of the population has got at least one vaccination shot.