The move comes only four days after Tokyo was placed on alert while the vaccination campaign has covered less than one per cent of the population.

The government is expected to official approve the alert status for Kanagawa, Saitama and Chiba and Aichi prefectures in central Japan at a meeting later on Friday.

It will allow heads of the prefectures to mandate shorter hours for bars and restaurants, along with punishments for violators and compensation for those who comply.

The measures are to begin Monday and continue through May 11.

Many of the cases have been linked to nightlife and dining spots, but they have recently spread to offices, elderly care facilities and schools.

Japan added some 4300 cases on Wednesday for a total of about 500,000 with 9500 deaths.

Prime Minister Yoshihide Suga said the measures cover the areas hit by rapid spikes fuelled by a new virus variant first detected in the United Kingdom.

"The government will respond firmly even during my US trip," he said before departing for Washington for talks with President Joe Biden.

Suga's government has been criticised for being too slow in enacting anti-virus measures out of reluctance to further damage the economy.

The surge has also prompted concern among many Japanese about hosting the Tokyo Olympics.

On Thursday, two top officials said there was a possibility the Games could be cancelled or even if they proceed, it might be without fans.

The new alert comes with binding orders but only for businesses to close early while measures for residents are only requests, leading some experts to doubt their effectiveness.

Osaka recently declared a medical emergency after its hospitals became overwhelmed with new cases and has moved next week's Olympic torch relay there off public roads.

Australian Associated Press