A Government text message urging people to stay at home and providing details of the new coronavirus lockdown rules is being pushed out across the UK.
Some mobile phone users have reported already receiving the text, with more expected to see it throughout the day.
It comes after Prime Minister Boris Johnson put Britain on lockdown on Monday evening as he outlined strict new measures to curb the spread of Covid-19, ordering people to only leave the house for a few specific reasons.
The text sent reads: "GOV.UK ALERT CORONAVIRUS. New rules in force now: you must stay at home. More info and exemptions at gov.uk/coronavirus Stay at home. Protect the NHS. Save lives."
Because the UK does not have an emergency alert system, network operators are sending out the text on behalf of the Government, resulting in it arriving at different times.
Trials of a text alert system were run in 2014 and were apparently successful, with a final report highlighting strong public support for the idea.
The report also concluded that such a system would be "an effective way of getting people to take specific protective action during an emergency", though it was never implemented.
South Korea's success in slowing the spread of Covid-19 has been at least partly attributed to an aggressive text messaging system deployed by the country, where alerts were sent out detailing the movements of people who had tested positive.
In the UK, the NHS has also started to send out messages to people it recognises as most vulnerable to the virus and urged them to remain at home for at least 12 weeks.
But the alerts come as cyber security experts encourage people to be aware of potentially malicious texts and emails, where criminals pose as official agencies to try and elicit personal information from users.
The UK's National Cyber Security Centre (NCSC) has warned of increased activity of this type, highlighting incidents where clicking on links in bogus emails claiming to have important updates has led to devices being infected.
These "phishing" attempts can lead to victims being left out of pocket or stripped of sensitive data.
NCSC operations director Paul Chichester said: "We know that cyber criminals are opportunistic and will look to exploit people's fears, and this has undoubtedly been the case with the coronavirus outbreak.
"Our advice to the public is to follow our guidance, which includes everything from password advice to spotting suspect emails."