Facebook users who have read, watched or shared false coronavirus content will receive pop-up warnings as the company attempts to combat the spread of misinformation.
The new alerts system is a response to what the World Health Organisation calls the "infodemic" around Covid-19.
An independent study suggests that the platform "sits at the epicentre of coronavirus misinformation".
Facebook says the research does not reflect the work it has done recently.
The California tech firm says it will start showing the messages at the top of news feeds "in the coming weeks".
Truth redirect The messages will direct people to a World Health Organisation webpage where myths are debunked.