Osaka confirmed on Tuesday a single-day record of 719 cases of the novel coronavirus, even as the western Japan prefecture has toughened measures in an attempt to stem a sharp rebound in infections.

The local government is set to declare a state of medical emergency on Wednesday as the occupancy rate of hospital beds in the prefecture has been nearing 70 percent, with the number of COVID-19 patients in serious condition increasing rapidly.

"If this continues, we will be on the verge of a medical collapse," Osaka Gov. Hirofumi Yoshimura told reporters Tuesday.

While daily infection figures for Osaka Prefecture have been the highest in the country in recent days, health minister Norihisa Tamura warned that the situation in Tokyo is also worsening and urged residents, business operators and health care workers to remain vigilant.

Tokyo on the same day confirmed 399 new cases, bringing its cumulative total to 123,350, the highest among the nation's 47 prefectures.

The nationwide daily increase totaled around 2,650 as of late Tuesday.

With the number of infections in Tokyo trending upward since mid-March, the seven-day rolling average rose to 396.9 per day, up about 10 percent from the previous week, according to the metropolitan government.

Although the rise in daily infections in Tokyo is not as sharp as in Osaka, Hyogo and Miyagi prefectures designated recently as being on the brink of a state of emergency, Tamura said at a press conference the situation in the capital warrants "extreme caution."

He warned that a surge in the Tokyo metropolitan area could affect the whole country.

Yasutoshi Nishimura, the minister in charge of the nation's coronavirus response, said the same day in an interview with Kyodo News that the government will seek to introduce a "circuit breaker," or a new set of indicators designed to promptly request businesses to shorten operating hours.

Under the current scheme, longer procedures are required such as approval at a panel of experts in infectious diseases and explanations in parliament before issuing a legally binding request.

Nishimura said closing restaurants and bars by 8 p.m. has been effective among other measures to curb the risk of infections.

The minister will discuss details of the new indicators with a government panel of experts, he added.

The government can declare a state of emergency when the situation reaches Stage 4, the highest level on its four-point scale. The threshold for quasi-emergency measures, on the other hand, is Stage 2.

Under the quasi-emergency designation, which became possible after a revised law took effect in February, authorities can implement tougher COVID-19 measures in targeted cities and towns, rather than doing so on a prefectural basis.

As the quasi-emergency measures commenced officially in the three prefectures on Monday, restaurants and bars in six major cities are asked to close by 8 p.m. and could be fined up to 200,000 yen ($1,800) for noncompliance.