Japan expanded COVID-19 restrictions to the capital Tokyo and a dozen regions encompassing half of the population on Wednesday, as the Omicron variant of coronavirus spurred record new infections.

The measures, which are already in force in three regions and set to run from Friday until February 13, were made public by Prime Minister Fumio Kishida after receiving approval from an expert panel earlier in the day.

"We are fighting an unknown virus, and I hope that we will be able to overcome this situation with adequate preparation and without excessive panic," Kishida said.

The quasi-emergency measures, as they are known, allow governors to restrict mobility and business activity by limiting the hours of operation of bars and restaurants and prohibiting the sale of alcohol.

According to a tally, Japan added more than 32,000 new COVID-19 infections on Tuesday, exceeding an August high shortly after Tokyo hosted the Summer Olympics.

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On Wednesday, Tokyo set a daily record with 7,377 new infections, while Osaka set a record with 6,101. The pandemic has resulted in a total of 1,924,937 cases and 18,436 fatalities in the country.

Although Omicron appears to cause less serious illness than previous variants, public health experts are concerned that a surge of such cases could overwhelm the healthcare system.

During the pandemic, Japan declared four states of emergency and vaccinated roughly 80% of its 126 million population, however its booster dosage programme only reached 1.2%.

After it appeared that base outbreaks of Omicron had spread into surrounding communities, Japan implemented quasi-emergency restrictions this month in three regions hosting US military sites.

On Wednesday, the occupancy rate of hospital beds for COVID-19 patients in Tokyo increased to 25.9%, according to authorities. Officials have stated that an increase of 50% would necessitate the declaration of a full state of emergency.