The number of Covid-19 infections in Tokyo may have jumped by nine-fold since last summer, coronavirus antibody tests showed, as Japan tries to rein in the country's third and most lethal wave of the pandemic ahead of the Olympics in July.

Random testing on people in Japan's capital in December showed that 0.91 per cent had antibodies to the virus, compared with about 0.1pc in a similar study in June, health ministry said in a report.

The study sampled more than 15,000 people and also showed increases in antibody rates in Osaka and Miyagi Prefecture. Reported infections in Japan have trended down in recent days but the government has signalled it would remain cautious, Reuters reported.