Japan on Friday acted to contain a record surge in COVID-19 cases with a return to curbs that have shown diminishing results, while a laggard vaccine booster program leaves many people vulnerable to breakthrough infections.

The government empowered authorities in Tokyo and 12 other prefectures to implement guidelines on mobility and business activity under a quasi-emergency — measures that, with three prefectures already under such devolved restrictions, now cover half of Japan's population.

The highly infectious omicron variant has driven the current wave of cases, and nationwide infections hit an all-time high of around 46,000 on Thursday.