Hong Kong police said they defused a pipe bomb and arrested four men for manufacturing explosives after raiding an apartment where they found protest-related items such as Guy Fawkes masks and protective gear.

Police also searched a village house in a northern neighbourhood where they found laboratory equipment they suspect could be used for producing explosives. The arrested men were aged between 21 and 29, a senior officer said late on Tuesday.

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Police have reported several discoveries of guns and explosives in recent months amid continuing pro-democracy protests that escalated in June over a now-withdrawn bill that would have allowed extraditions to China.

In a separate statement on Wednesday, the government said it cancelled its usual Lunar New Year fireworks display on Victoria harbour, which was supposed to take place on January 26, citing "public safety considerations".

Senior Superintendent Chan Tin-chu told reporters that the discovered bomb was 20 centimetres (8 inches) long and weighed 680 grammes (1.5 pounds). A controlled explosion produced shrapnel that left a hole in the metal door of a lift in the building, he said.

"If the bomb was ... thrown at a car, all the people inside the vehicle would definitely die," Chan said.

Those arrested were suspected of being members of an anti-government protest group, he said.

Three of the men were tertiary students and were also charged with illegal assembly on New Year's Day.

In early December, police said officers had defused two homemade bombs found at a centrally located school.