TOKYO (REUTERS) - Coronavirus cases in the Greater Tokyo area are showing signs of creeping up, Japanese Health Minister Norihisa Tamura said on Friday (March 12), raising questions about whether a state of emergency could be lifted on schedule on March 21.

The Japanese government last week extended the emergency declaration for Tokyo and three neighbouring prefectures by 14 days, saying Covid-19 cases hadn't fallen far enough, while new, more infectious coronavirus variants posed a threat.

A decision on whether the state of emergency could be lifted in the Tokyo area, which accounts for about 30 per cent of Japan's population, would ultimately be made after hearing the views of experts, Mr Tamura said in televised remarks.

"Lifting the measures will be based on putting in place a system to ensure there's not a rebound in cases," he said.

Restrictions such as shorter business hours for restaurants and bars have helped diminish new cases in Tokyo to roughly a tenth of a peak of 2,520 cases on Jan 7.

But the numbers are far from Tokyo Governor Yuriko Koike's target of bringing the seven-day average to 70 per cent of the preceding week.

"The number of new positive cases has stopped decreasing, and we need to be very vigilant about the possibility of a resurgence due to mutated strains," Ms Koike said on Friday during a meeting with health experts.

The seven-day average of new cases in Tokyo has been stuck in the mid- to high-200s since late February, while the daily tally exceeded 300 for the second straight day on Thursday.

Tokyo - and Japan - are racing to bring coronavirus cases under control and vaccinations well under way as it prepares to host the Summer Olympics, which start July 23.

Japan's Covid-19 inoculation campaign began only last month with health workers and has been moving slowly, hampered by a lack of supply.

The country has so far recorded about 441,000 coronavirus cases and 8,400 deaths.