HONG KONG, Jan 15 — 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 men were aged 21-29, a senior officer said late yesterday.

The bomb was 20 cm long and weighed 680 grammes. The controlled explosion produced shrapnel that left a hole in the metal door of an elevator in the building, Senior Superintendent Chan Tin-chu told reporters.

"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.

Police have reported several discoveries of guns and explosives in recent months as pro-democracy protests that escalated in June over a now-withdrawn bill that would have allowed extraditions to China have kept a relentless pace. — Reuters