Instagram has been blocked on the mainland, meaning that images such as these can’t be seen there.
Weibo, China’s version of Twitter, which is constantly monitored by the government, has seen an unprecedented number of posts deleted.
Many Hong Kong protesters switched from internet-based messaging services to FireChat, which doesn’t require an internet connection, in anticipation of a shutdown.
The app was downloaded around 100,000 times in 24 hours at the weekend. Up to 33,000 people were using it in Hong Kong at once, according to Open Garden, the company that developed it.