A new smartphone app to alert users to possible terror attacks was launched by the French government on Wednesday in time for the start of Euro 2016, amid growing security concerns over the tournament.

The application, which is free to download in both French and English, will send users a warning "in case of a suspected attack," said the interior ministry, which has piloted and introduced the service.

It will also alert users -- who must agree to be geolocated -- about "unexpected events" such as the breaching of flood defences.

Alerts will appear on the app less than 15 minutes after the incident has been confirmed by authorities, and will be customised according to the user's exact location.

The government said the app was developed after November's jihadist attacks in Paris -- including on the main stadium -- which killed 130 people.

On Tuesday, Britain warned fans going to France for the football championships there was a "high threat from terrorism" and that stadiums, fan zones and transport hubs were potential targets.

The month-long tournament kicks off on Friday and is expected to attract two million visitors to France.

Users of the app will also be able monitor alerts for up to eight different geographical zones, allowing them to check on family members or friends.

It will also provide advice on how to stay safe, with information tailored to each particular situation, the ministry added.

The government hopes the app will help users -- or app "ambassadors" as it calls them -- spread reliable, official information about the security situation across social media.

This could help prevent France's emergency services hotlines from becoming overwhelmed, said Interior Minister Bernard Cazeneuve, adding the app would "keep the public up to date with what we know."

Although it was launched for Euro 2016, it will be developed further after the tournament.