German police drew criticism Tuesday for using an app to trace contacts from bars and restaurants in the fight against the pandemic as part of an investigation. 

The case stemming from November last year began after the fatal fall of a man while leaving a restaurant in the western city of Mainz.

Police seeking possible witnesses made use of data from an app known as Luca, which was designed for patrons to register time spent in restaurants and taverns to track the possible spread of coronavirus.

Luca records the length of time spent at an establishment along with the patron's full name, address and telephone number -- all subject to Germany's strict data protection laws.

However the police and local prosecutors in the case in Mainz successfully appealed to the municipal health authorities to gain access to information about 21 people who visited the restaurant at the same time as the man who died.

After an outcry, prosecutors apologised to the people involved and the local data protection authority has opened an inquiry into the affair.

"We condemn the abuse of Luca data collected to protect against infections," said the company that developed the Luca app, culture4life, in a statement. 

It added that it had received frequent requests for its data from the authorities which it routinely rejected.

Konstantin von Notz, a senior politician from the Greens, junior partners in the federal coalition, warned that abuse of the app could undermine public trust.

"We must not allow faith in digital apps, which are an important tool in the fight against Covid-19, to disappear," he told Tuesday's edition of Handelsblatt business daily.