The city is on its highest coronavirus alert level, with experts warning infections appear to be spreading rapidly and widely.

"The infections are spreading not only among young people but also among middle-aged and older people," Tokyo Governor Yuriko Koike said during a meeting with infectious disease experts.

"I'd like to ask [Tokyo residents] to refrain from going out as much as possible, especially elderly people and those with pre-existing conditions," she said ahead of the holiday weekend.

Tokyo hit a new daily record of 293 cases last week, and the figure has stayed above 200 in recent days.

Koike said the city was seeing infections at restaurants and theatres, not just nightlife areas as in previous weeks. Clusters have also been reported at workplaces and schools.

Japan has had just over 26,300 cases and close to 1,000 deaths since the disease was first detected in the country.

The figure is low compared with countries worst hit by the pandemic, but Japanese experts said the number of patients in serious condition was gradually increasing and warned medical workers were exhausted by growing workloads and demoralized by low pay.

Japan will begin a four-day holiday from Thursday, with Friday the day that the now-postponed Tokyo 2020 Olympics would have opened.

The Games are now set to begin on July 23, 2021, and organizers will hold a small-scale year-to-go celebration on Thursday, but without any spectators, in light of the rising number of cases.

The increasing number of daily cases in the capital has also prompted the government to exclude Tokyo residents from a nationwide program to subsidize domestic tourism.

Prime Minister Shinzo Abe lifted a nationwide state of emergency in late May and appears to have little appetite to reintroduce it, with the economy suffering its first recession since 2015.