Newly minted deputy PM Oliver Dowden has said no action would be needed when it goes off at 3pm today, but in the future it might be the "sound that could save your life".

The system is designed to warn the public if there is a danger to life nearby, mirroring similar systems used in the Netherlands, the US and Canada.

It will last for about 10 seconds at 3pm, with the alert being sent to every 4G and 5G device across the UK.

The plan is to use it to alert people to life-threatening situations including floods and wildfires.

Mr Dowden said: "Keep calm and carry on - that is the British way and it is exactly what the country will do when they receive this test alert at 3pm today.

"The government's number one job is to keep people safe and this is another tool in the toolkit for emergency situations, such as flooding or wildfires, and where there is a genuine risk to life.

"So it really is the sound that could save your life.

"I would encourage people to remember that today it is just a test; there is no need to take any action and you can simply swipe it away as you would any other message you receive."

People are able to opt out in their device settings, but officials hope users will keep them on.

Phones that are off or in airplane mode will not receive an alert.

Those who receive the alert will be prompted to acknowledge its arrival by swiping or clicking the message before being able to continue using their devices.

Read more:
Everything you need to know about the emergency alert test
Emergency alerts in other countries - and times they've gone wrong…

The entertainment and sport sectors are planning how to guard against disruption to large events when the test goes off.

Organisers of the World Snooker Championship will pause play just before 3pm at the Crucible in Sheffield and it will resume after the alarm.

The Society of London Theatre said it had shared the government's guidance with its members and advised them to tell attendees to turn off their phones to "minimise disruption to shows".

For cinema-goers, a Vue spokesperson said: "Before every screening at Vue, we encourage our customers to turn their mobile phones off in order to fully immerse themselves in the big screen experience."

The St George's Day test coincides with major sporting events including the London Marathon and Premier League ties between Bournemouth and West Ham, and Newcastle and Tottenham Hotspur, kicking off at 2pm.

Officials said they have worked with the Football Association and the marathon's organisers to make sure the test's impact will be limited.

Motorists have been warned it will still be illegal to pick up their mobiles during the test, with caught holding a phone behind the wheel facing six penalty points and a £200 fine.

Domestic violence campaigners also warned the alert could put people in danger by revealing the location of secret phones hidden by those at risk.