Both platforms took down hundreds of accounts that originated in mainland China, where the services are blocked, that claimed the protesters were acting violently and accused them of ulterior motives. One Facebook post likened them to ISIS fighters.

“We’re constantly working to detect and stop this type of activity because we don’t want our services to be used to manipulate people,” said a statement from Facebook’s head of cybersecurity.

Another angle: A buildup of paramilitary troops in Shenzen is a stark reminder that the use of force remains an option for Beijing, and experts say that it is likely that President Xi Jinping has already completed preparations for an intervention.

Related: To much of the world, Pepe the Frog is a hate symbol. But the cartoon character has been adopted by Hong Kong protesters, who are largely unaware of its alt-right connotations.