Facebook Inc said on Thursday it will take down misinformation about China's fast-spreading coronavirus in a rare departure from its approach to health content, after the World Health Organisation declared the outbreak a global health emergency.

The world's biggest social network said in a blog post that it would remove content about the virus “with false claims or conspiracy theories that have been flagged by leading global health organisations and local health authorities”, saying such content would violate its ban on misinformation leading to “physical harm”.

The move is unusually aggressive for Facebook, which generally limits the distribution of content containing health misinformation through restrictions on search results and advertising, but allows the original posts to stay up.

That approach has angered critics who say the company has failed to curb the spread of inaccuracies that pose major global health threats.

In particular, misinformation about vaccination has spread far on social media in many countries in recent years, including during major vaccination campaigns to prevent polio in Pakistan and to immunise against yellow fever in South America.

Facebook, under fierce scrutiny worldwide in recent years over its privacy practices, has previously removed vaccine misinformation in Samoa, where a measles outbreak killed dozens late last year, after determining the situation was so severe that the inaccuracies were risks to physical harm, a spokeswoman told Reuters, calling the move an “extreme action”.

It also removed misinformation about polio vaccines in Pakistan, although the imminent harm in that case involved risks of violence against the health workers carrying out the immunisation campaigns, she said.