China’s most popular messaging app has been censoring key words about the coronavirus outbreak from as early as 1 January, a report has found.

Toronto-based research group Citizen Lab found that WeChat blocked combinations of keywords and criticism of President Xi Jinping.

The report also found that WeChat, owned by Chinese firm Tencent, blocked more words as the outbreak grew.

China has for years censored what its people read and say online.

But this report suggests China began censoring discussions weeks before officials began acknowledging the severity of the outbreak.

It was on 31 December that China first alerted the World Health Organization to an outbreak of a new coronavirus in the city of Wuhan.

But authorities initially withheld information from the public – under-reporting the number of people infected, downplaying the risks, and failing to provide timely information that could have saved lives.

It was only on 20 January that Chinese president Xi Jinping publicly addressed the issue of the virus, saying it had to be “resolutely contained”.

It’s not clear if the social media platforms blocked these keyword combinations based on government directives – or if it was done of its own accord.

However, the report suggests that it could be the result of companies “over-censoring in order to avoid official reprimands”.

Authorities have confirmed more than 92,000 cases of the virus worldwide – of which more than 80,000 are in China.

WeChat was found to have censored 132 keyword combinations between 1 – 31 January. As the outbreak continued, WeChat censored 384 new keywords between 1 – 15 February.

These include keywords that referenced Chinese leaders – including President Xi – as well as neutral references to government policies on handling the epidemic, and responses to the outbreak in Hong Kong, Taiwan and Macau.