Japan's Covid-19 tracking application for some smartphone users has had a malfunction since September and has failed to pass on some notifications of suspected contact with people infected with the virus, the health ministry said on Wednesday.
The ministry did not say if the problem, which came with an update of the app, had contributed to the spread of the virus but it said it was working to fix it by the middle of this month.
"I am truly sorry for the inconvenience caused and for the loss of trust," state broadcaster NHK cited the health minister, Norihisa Tamura, as saying.
NHK reported that the bug affected about 30% of Android phone users.
The app, named COCOA for Contact-Confirming Application, was designed by Microsoft Corp and is available for Apple Inc's iPhone as well as devices using Google's Android software.
The programme has been downloaded almost 25 million times in Japan since its launch last summer and has recorded about 10,000 positive coronavirus cases, according to ministry data.
It uses Bluetooth signals to detect contact with nearby users lasting 15 minutes or more. If a user later tests positive for the virus their contacts can be traced and notified through the programme.
The Android-related bug failed to deliver notifications of those contacts, the ministry said in a statement.
Japan has had 390,000 cases of the coronavirus and 5,794 deaths and is desperate to stamp out flare-ups of infection as it prepares for the summer Olympic Games, due to begin on July 23.