Tokyo officials say they confirmed 545 new cases on Thursday, following 555 the day before, and governor Koike Yuriko says it is time to tighten the rules again.
"We have asked the central government to designate Tokyo as an area where strict measures should be taken," she said on Thursday.
Prime Minister Suga Yoshihide has said he intends to approve the request. The government is also taking a close look at conditions in Kyoto and Okinawa, including the availability of hospital beds, and concerns about virus variants.
The new measures are expected to begin Monday and run until May 11 in Tokyo. Officials plan to urge bars and restaurants in certain areas to close earlier, and will ask residents to refrain from unnecessary travel outside the prefecture.
A metropolitan government panel assessing the outbreak met on Thursday. Medical experts at the session expressed strong concern about a potentially explosive spread of the virus.
They said about a third of 158 positive samples taken recently had N501Y mutations. The strain was first detected in the UK, and had spread mainly in western Japan.
"The ratio of N501Y has sharply increased over the past week. I believe the variant is currently a bigger threat," said Yoshimura Kazuhisa of the Tokyo Metropolitan Institute of Public Health.
Tokyo's leaders also released estimates on how cases would rise if they followed three different rates: an increase of 1.1 times, 1.2 times, and 1.5 times over a week. In the case of the fastest pace, the daily count would likely exceed 1,000 on April 22, 2,000 in early May, and 4,000 in the middle of May.
Osaka declares medical "red alert"
Osaka Prefectural officials reported 905 cases on Thursday, a record number for a third consecutive day. More than 90 percent of hospital beds for serious COVID-19 patients there are occupied. The prefectural government declared a medical "red alert" on Wednesday.
Staff at an emergency care center in Higashiosaka City say they are overwhelmed. Osaka Prefectural Nakakawachi Emergency and Critical Care Center has eight beds for seriously ill patients. They were all empty at one point in mid-March, but have been fully occupied since Tuesday.
The center's director, Yamamura Hitoshi, says this wave of the virus appears to have different characteristics.
"The average age of seriously ill patients was in the 70s during the previous wave, but we see more younger age brackets this time," he says. "People who are becoming very ill this time are neither obese nor have preexisting conditions such as diabetes."
He also says that the average length of hospitalization is three to four days longer than it was previously.
"The biggest crisis ever"
Nationwide, 3,447 new infections were reported on Thursday.
Nakagawa Toshio, the head of the Japan Medical Association, describes the current situation as the biggest crisis since the outbreak began.
"The public is getting used to living with the virus and reaching the limit of their patience in terms of refraining from going out or operating businesses," he said at a news conference on Wednesday. "The situation is very serious and we are on the brink of the level that requires another state of emergency to be declared."