The app is being trialled in Liguria, Puglia, Marche and Abruzzo and will later be rolled out nationwide, possibly by next Monday, June 15.

“We’re starting with a test that will last several days and then, next week or the week after, it will be extended to everyone,” Deputy Health Minister Pierpaolo Sileri said.

Authorities didn’t explain why those regions in particular were chosen for the trial.

The launch of the app had been delayed amid concerns about users’ privacy, and some local authorities doubt how useful it will be.

Many critics point out that it won’t be effective unless a large enough percentage of the population downloads it.

In Puglia, for example, local health authorities say the app will need to be downloaded by at least 10 per cent of local residents for it to be effective.

But authorities say the app is being well received, with some 500,000 downloads reported within 24 hours after it was made available on the Apple and Google stores on June 1.

Each smartphone with the app installed will emit regularly an anonymous ID code that can be detected within a few metres by other smartphone users with the same app.

If one of the app-users reports that they have tested positive for the coronavirus, the system makes it possible to inform the people with whom they have been in close contact over previous days.

The codes are anonymous, and don’t contain personal information about the users, health authorities said.

“It is an innovative, technological support to the initiatives the government has already put into place to limit the spread of the COVID-19 virus,” a joint statement by the ministries of health and of innovation and the premier’s department said.

“It was developed in compliance with Italian and European legislation to protect privacy.”

Data collected will be stored on the device, not on a central server.

The system will not trace movements and data can only be shared with the user’s permission.

Any data collected and shared with the central server will be deleted by December 31, 2020.

Italy has recorded 33,964 deaths from coronavirus since the outbreak began in February, and around 235,000 people have tested positive for the virus.