Japan's health ministry says the number of seriously ill coronavirus patients using ventilators or receiving intensive care treatment was 2,223 nationwide on Saturday.
The number is the highest to date, two more than the previous record set on Friday.
The Japanese government on Saturday began inoculating younger people aged 18 to 39 at its large-scale coronavirus vaccination site in central Tokyo.
The government plans to administer about 22,000 doses preferentially to people between those ages through September 25.
All available slots were filled in about two hours after officials began to accept requests for reservations at 6 p.m. on Friday.
A 23-year-old woman visited the site on Saturday after she made a booking.
She said that she felt relieved as she had tried to make a reservation many times, but had been unsuccessful.
A 23-year-old man who visited the site for his second shot said that many of his friends from his same age group had been unable to get an appointment for vaccines provided by municipal governments.
He said that anyone who wants to get inoculated should be able to do so.
The government will operate the vaccination site until the end of November, about two months longer than initially planned.
It is one way in which it aims to accelerate the vaccine roll-out.