Hong Kong - Hong Kong police arrested four men after a raid that uncovered explosives and a pipe bomb, government-backed broadcaster RTHK reported on Wednesday.
Police found what they called "protest-related materials" in a raid on Tuesday evening at a flat in Mong Kok, a densely populated residential area known for its outdoor markets and shopping areas.
Police also searched a house in Sheung Shui, a town close to Hong Kong's border with mainland China, which they suspect was being used a laboratory for producing explosives, according to RTHK.
The pipe bomb said to contain around 40 grams of explosives was detonated by bomb disposal experts, which caused some damage to the building.
Police senior superintendent Chan Tin-chu said the bomb was "very powerful" and that a small explosion occurred while it was being defused.