Questions have been raised over a smartphone app being developed to track foreign visitors' whereabouts during the Tokyo Olympics and Paralympics, due to its hefty cost and the amount of work left to do with five months to go.

Japan is to decide by the end of spring on the number of spectators at each venue and whether to accept fans from overseas. The app is seen as a disease control "lifeline," according to a games source, should overseas fans be allowed into the country.

A company made and won the bid in January to develop the app for ¥7.3 billion ($69 million) — way before the decision is made.