Japan on Friday reported its first cases of a fast-spreading variant in passengers arriving from Britain. The new variant has also been detected in a man who visited the UK and a family member — the first cases of infected people found outside airport checks — Nippon TV reported on Saturday.
The new strain adds to worries about a surge in cases as Tokyo reported another record rise on Saturday.
Infections of the virus that causes Covid-19 hit a record 949 in the capital just as Japan heads into New Year holidays that normally see people stream from the capital into the provinces.
Serious cases were unchanged from a day earlier at 81.
Tokyo transport hubs were subdued, local media said, a day after Prime Minister Yoshihide Suga, under pressure as cases continue to climb, urged the nation to stay home and avoid social mixing.
With New Year celebrations centred on family gatherings and mass visits to temples and shrines, experts have warned public restraint will be essential to prevent infection rates from rising further amid concerns of pandemic fatigue.
Suga's initial political honeymoon after taking his post in September has ended, with his popularity sliding after criticism he was slow to react to rising infections in Tokyo and for attending a group steak dinner in defiance of his own calls for caution.