The tougher measures effective for one month until May 5, cover Osaka, Hyogo and Miyagi prefectures, with prefectural authorities requesting restaurants and bars to shorten their opening hours and close by 8 p.m. and customers asked to wear masks while conversing, reports Xinhua news agency.
The revised law enables the central government to declare a situation that falls short of a state of emergency in which special measures can be taken to counter the spread of the virus.
The stronger measures that can be taken by the three prefectures could include imposing fines on bars and restaurants that ignore requests to shorten their operating hours.
Businesses are also urged to promote remote working for their employees, and large spectator events will have had the numbers of attendees capped at 5,000.
The designation as being on the verge of a state of emergency can be applied when infections are surging in a situation equivalent to Stage 3, the second-highest on the government's four-tier alert system.
Osaka and Miyagi prefectures have already reached Stage 4, the highest on the government's alert scale, based on the the volume of weekly infection cases per 100,000 people.
Hyogo prefecture is at Stage 3, the Health Ministry said on Monday.
Osaka has witnessed the daily tally surpass those of Tokyo, the epicentre of the pandemic in Japan.
Tokyo on Monday reported 249 new Covid cases, while Osaka confirmed 341 infections.
On Sunday, cases in Osaka stood at 593, a day after hitting a single-day record of 666 infections, according to the health ministry and local authorities.
"The virus is rapidly spreading in the central areas of the three prefectures," Yasutoshi Nishimura, minister in charge of the nation's virus response, said on Monday.
"We will swiftly utilise the stronger measures to prevent it from spreading to the entire region," he said.
On March 30, the central government granted the requests of the three prefectures to take the stronger measures and be designated as being on the verge of a state of emergency under a revised law that took effect in February.