Japan started to vaccinate its elderly against the coronavirus on Monday amid growing concerns about another wave of new infections.
The country would inoculate about 36 million people aged 65 and above, which accounted for 29 per cent of its population.
Since its launch in mid-February, the roll-out of COVID-19 vaccines had been extremely slow. Only 0.4 per cent of the population has been fully vaccinated as of Friday, according to the Ministry of Health, Labour and Welfare.
Also on Monday, the government extended a semi-state of emergency to Tokyo, Kyoto and Okinawa prefectures as the regions have seen an increasing number of new coronavirus cases due to the rapid spread of new variants of the virus.
Tokyo, which would stage the postponed Olympic Games in less than four months, confirmed 421 new infections on Sunday after exceeding 500 new daily cases for the fourth consecutive day.
Japan has so far reported about 507,600 known infections and more than 9,400 deaths related to COVID-19, according to a tally by broadcaster NHK.
The central government adopted the semi-state of emergency in Osaka, Miyagi and Hyogo prefectures a week ago.
Prime Minister, Yoshihide Suga, told reporters on Friday that new variants constituted about 70 per cent of the infections in the western prefectures of Osaka and Hyogo and about 20 per cent in Tokyo.