Sweden currently has an outdoor alarm system consisting of around 4,500 horns on rooftops and other tall buildings throughout the country.

"Based on the experiences we've seen in Ukraine, we've seen that the enemy, in this case Russia, would shoot down our outdoor warning system," Henrik Larsson, head of the population protection department at the Swedish Civil Defence and Resilience Agency, told AFP.

"So this would complement that," he said of the new system, dubbed SE Alert.

In the event of an air raid, cellphones connected to the Swedish telecoms network would automatically emit voice message warnings, sirens and begin vibrating, he said.

The system, to be rolled out within six months, could also be used to send alerts in case of major crises during peacetime, such as nuclear or chemical accidents.

Larsson said the agency was also working with the Swedish armed forces to develop an app that lets people easily photograph airborne drones and report them to authorities.

Sweden has been beefing up its civil preparedness and so-called "total defence" measures since Russia's full-scale invasion of Ukraine in 2022.

The idea is to mobilise all of society, from authorities to citizens and businesses, to collectively resist armed aggression while maintaining essential functions.