More than 500,000 people were “pinged” by the NHS Test and Trace app in a week.
A sum of 520,194 alerts were sent to users of the app.
The alert warns them they have been in close contact with someone who has tested positive for Covid-19.
People receiving the warning must self-isolate.
The number of “pings” has increased by 46% over a week.
The rapid rise is causing concern in industry and public services as more and more workers stay at home.
Communities Secretary Robert Jenrick said the Government is “concerned” about the number of people off work due to being “pinged” by the app.
He added: “It is important that we have the app, that we take it seriously, that when we do get those messages, we act accordingly.”
Meanwhile tens of thousands of Test and Trace users are switching off the app to avoid being caught.