Japan began vaccinating front-line health workers and elderly people in February, but the slow pace compared with other major industrialised nations has spurred calls for the Tokyo Games to be delayed again or cancelled.

Opening up vaccinations to most citizens may help the government ease concern the country is unprepared to host tens of thousands of foreign athletes and Olympic officials as its healthcare system struggles with a fourth wave of infections.

Vaccinations have mostly been left to local health authorities to carry out with some cities and towns vaccinating residents faster than others.

The Tokyo vaccination centre will also begin taking appointments by telephone for the first time from Saturday, in addition to online bookings in a bid to encourage more people to get shots, the Sankei newspaper reported.

A spokeswoman at the Ministry of Defence, which operates the site, declined to comment on the telephone and did not immediately respond to an email.

Prime Minister Yoshihide Suga said on Wednesday Japan aims to finish vaccinating everyone who wants a shot by October-November. That may require about 1 million injections a day.

"I want to explain to the G7 about our measures to tackle infections and our intention to hold a safe and secure games and win their understanding," Suga told reporters as he left his residence in Tokyo for a G7 meeting in Britain.

Politics and money

With less than 50 days before the Olympics open, Japan has vaccinated just over a tenth of its population with at least one dose.

Organisers will this month decide whether to allow people in Japan to attend events. Spectators from abroad are not allowed.

The Games have become a big political issue for the government given widespread public opposition to holding them during the pandemic.

The financial stakes are also huge.

The organiser estimates that the cost of the Olympics, including $3 billion resulting from last year's delay, will be more than $15 billion.

In a sign of continued concern about the risk of more infections during the Games, however, the governor of Chiba prefecture on Thursday cancelled plans for an outdoor Olympic viewing site in a park that would have drawn thousands of people.

"We have decided to cancel plans for the live site," Toshihito Kumagai told a press briefing.

Near Tokyo, Chiba is due to host four Olympic events - surfing, fencing, wrestling and taekwondo - and four Paralympic events. On Wednesday, the prefecture recorded 106 new COVID-19 cases compared with 440 in Tokyo.