Later, rioters attacked police officers with gasoline bombs, bows and arrows and metal balls.

During the melee, a police officer engaged in media liaison duties was shot in the calf with an arrow, police said.

Police severely condemned the violent acts and warned that anyone who stayed behind or assisted protesters could face rioting charges.

An anti-riot police officer was hit by metal balls on the visor of his helmet, but was not injured, police added.

Police advised the public to avoid the area because a large number of weapons, including flammable fluids, were stored on the campus.

On Saturday night, a spokesman for PolyU said several laboratories had been vandalized and some "dangerous" chemicals were stolen. The university reported the incident to the police, considering it a serious threat to public safety.