Authorities said a 20-year-old woman and a 26-year-old man posted the messages on social media on July 2 – a day after a police officer was stabbed and injured in Causeway Bay.
They were arrested in Tin Shui Wai and Sha Tin. Officers seized two smartphones as evidence.
Superintendent Tam Wai-shun from the police’s Cyber Security and Technology Crime Bureau said the operation is ongoing and there could be more arrests.
“The number of comments the persons have made is not the main thing that we consider on the arrests. The thing we consider is the seriousness of the comments,” he said.
He refused to be drawn on whether the police have classified the cases as terrorist attacks, but stressed the force will not turn a blind eye to those who try to incite hatred and violence on the internet.
Meanwhile, Police Commissioner Raymond Siu also warned people not to “glorify violence”, saying officers will enforce the law strictly.