TOKYO, Jan 19 (Reuters) - Japan on Wednesday widened COVID-19 curbs to the capital Tokyo and a dozen regions covering half the population as the Omicron variant of coronavirus drove record new infections.

Already in effect in three regions, the measures, set to run from Friday until Feb. 13, were made official by Prime Minister Fumio Kishida after getting the sign-off from an expert panel earlier in the day.

"We are battling against an unknown virus, and I hope that we can overcome this situation with sufficient preparation and without excessive fear," Kishida said.

The quasi-emergency measures, as they are called, permit governors to limit mobility and business activities, by shortening the operating hours of bars and restaurants, and barring sales of alcohol.

"While the measures won't be as effective as when numbers were smaller, I think they still can mitigate things," said Gautam Deshpande, a doctor at St. Luke's International Hospital in Tokyo.

"The horse is only half out of the barn at the moment."

Japan added more than 32,000 new COVID-19 infections on Tuesday, a tally by national broadcaster NHK showed, exceeding an August high soon after Tokyo hosted the Summer Olympics.

Tokyo set a daily record on Wednesday with 7,377 new infections, as did the western prefecture of Osaka, with 6,101.

The country has recorded a total 1,924,937 cases and 18,436 deaths from the pandemic.

Although Omicron is more infectious than previous variants it appears to cause less serious illness, but public health experts still worry that a wave of such cases could overwhelm the healthcare system.

Japan has declared states of emergency four times during the pandemic, and vaccinated about 80% of its population of 126 million, although its booster dose programme has reached just 1.2%.

Authorities have "dragged their feet with boosters," Deshpande added.

Japan rolled out quasi-emergency curbs this month in three regions hosting U.S. military facilities, after it appeared that base outbreaks of Omicron spilled into surrounding communities.

Tokyo's occupancy rate of hospital beds for COVID-19 patients, a figure closely monitored by authorities, rose to 25.9% on Wednesday. An increase to 50% would warrant escalation to a full state of emergency, officials have said.

In a sign that the pandemic is weighing on the economy, Toyota Motor Corp said it cancelled a factory line shift in Toyota City after eight workers there tested positive.

The Japan National Tourism Organisation said last year's 245,900 overseas visitors were the fewest on record, going back to 1964.

(Reporting by Rocky Swift, Kantaro Komiya, Chang-Ran Kim; Editing by Clarence Fernandez and Angus MacSwan)