Japan's government is set to extend a state of emergency in Tokyo and three other areas by about three weeks until the end of May to curb a surge in coronavirus cases just months before the start of the Tokyo Olympics.

The government had hoped a "short and powerful" state of emergency would contain a fourth wave of infection, but new cases in Tokyo and Osaka prefecture are still at high levels, said economy minister Yasutoshi Nishimura, who is also in charge of pandemic measures.

Extending the state of emergency to 31 May from 11 May will leave a margin of fewer than two months before the 23 July start of the Games, which were postponed a year due to the pandemic.

"Osaka particularly is in quite a dangerous situation with its medical system," Mr Nishimura said at the start of a meeting with a panel of medical and economic experts, noting that variant strains are spreading rapidly.

"We have a strong sense of danger that Tokyo could soon be turning into the same situation as Osaka."

The panel later approved the extension plan, Mr Nishimura said.

Formal government approval is set for later in the day, with Prime Minister Yoshihide Suga giving a news conference.

All hospital beds for critical patients in Osaka prefecture are occupied, public broadcaster NHK reported, and Mr Nishimura said the medical situation in neighbouring Hyogo prefecture, where the city of Kobe is located, was also poor.

In Tokyo, there were 907 new cases of novel coronavirus infection today.

Nationwide, Japan has recorded 618,197 cases of infection and about 10,585 deaths from Covid-19, the respiratory disease the virus causes, government figures showed.

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Mr Nishimura said the government aims to place Aichi prefecture, in central Japan, and Fukuoka prefecture in the southwest under a state of emergency - joining Tokyo plus Osaka, Hyogo and Kyoto prefectures, home to nearly a quarter of the population, and where current measures began on 25 April.

The northern island of Hokkaido and two other areas will be added to regions under a "quasi state of emergency," he added.

Under the extended state of emergency, bars, restaurants, karaoke parlours and other places serving alcohol will continue to be asked to stop offering alcoholic drinks, while people will continue to be asked to avoid taking unnecessary trips.

People wearing facemask on a busy shopping street in Kamakura

But other requests will be loosened, Mr Nishimura said.

Commercial facilities such as shopping centres, for instance, will be asked to shorten opening hours rather than close completely - though he noted that Tokyo and Osaka prefecture would make their own decisions based on local conditions.

Japan has not suffered as badly from the virus as other nations, but its vaccination campaign is significantly lagging, with even many elderly people still awaiting inoculation.

Still, Japan and the International Olympic Committee insist the Games will take place, though foreign spectators have been banned.

A decision on domestic spectators has yet to be reached.

Upcoming test events for the Olympics, including an athletics event at the weekend, will not be affected by the extension of the state of emergency.

Online petition calls for Olympics to be cancelled

An online petition calling for the Tokyo Olympics to be cancelled has garnered almost 200,000 signatures in the past few days, as public concerns mount over holding the Games in a pandemic.

In two days since its launch, an online campaign called "Stop Tokyo Olympics" has gathered more than 187,000 signatures, nearing its 200,000 goal and underscoring public concerns over holding the massive sporting event in Japan's capital.

Opinion polls in Japan have found a majority of the public is opposed to the Games, which are due to open on 23 July.

Kenji Utsunomiya, the online petition organiser, wrote on his website: "We strongly call for the prevention of spread of coronavirus and protection of lives and livelihood by using available resources to stop the Olympics."

Mr Utsunomiya is a lawyer who has run several times for Tokyo governor.