Some of the protesters were knocked to the ground in the incident at around 8am on Hing Fong Road.
Police said the officer in question was trying to come to the aid of his colleagues.
“A rioter sprayed an unknown liquid at a police officer’s face, causing temporary loss of vision. Later, one officer drove his motorbike to approach the site to render assistance, in an attempt to separate rioters and the police officers. During the process, the officer was attacked with a hammer,” said Chief Superintendent John Tse.
He added that the force understands it was a serious incident and said it accords high priority to the case.
“The officer has been suspended from all frontline duties instantly and has taken leave instantly. The case under investigation by the New Territories South region. If any misconducts arises, the police will certainly follow up,” Tse said.