HONG KONG – Hong Kong has a high risk of homemade bombs and the security bureau still take steps to guard against the risk of homegrown terrorism, said the city’s security chief John Lee Ka-chiu on Wednesday.

In response to queries by lawmakers, the secretary for security said police had cracked five cases involving homemade bombs since October last year. Five handmade bombs and a large cache of bomb-making materials had been seized, Lee said.

On Tuesday, three men aged 21-29 were arrested on suspicion of manufacturing explosives after police found 40 grams of explosives in a flat in Mong Kok.

Police defused the pipe bomb at the scene, where they also found protest-related items such as Guy Fawkes masks and protective gear.

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

Senior Superintendent Chan Tin-chu, Hong Kong Police Force

The bomb was 20 cm long and weighed 680 grams. 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.

Police also searched a village house in a northern neighborhood where they found laboratory equipment they suspect could be used for producing explosives. 

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

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Police have reported several discoveries of guns and explosives in recent months as anti-government protests that escalated in June over a now-withdrawn extradition bill continued.

Three universities — City University, Chinese University and the Polytechnic University —  have also reported cases of missing corrosive and flammable chemicals from their labs.

It is suspected that the chemical had been stolen to make explosive devices and gasoline bombs.

No one has been arrested yet in relation to the missing chemicals, Lee said.

Lee has pledged to step up efforts in guarding against homegrown terrorism, adding that the government will take various measures to raise public awareness of the risk.

With contribution from Li Bingcun