Japan has granted fast-track approval to US drug maker Pfizer Inc's Covid-19 pill, the heath minister said, as the country struggles to slow fast-spreading omicron infections.

The approval came less than a month after Pfizer applied in mid-January, an exceptional speed in a country where foreign drug approvals usually take much longer.

Health Minister Shigeyuki Goto said the availability of Pfizer's Paxlovid pill gives high-risk patients, including elderly people and those with underlying health issues, greater treatment options.

The approval comes as surging cases among elderly patients are starting to overwhelm hospitals in Tokyo and other metropolitan areas, and delayed booster vaccinations have reached only about eight per cent of the population.