The police said explosives were discovered in a raid at a suspected bomb-making unit on Friday. A 27-year-old man was arrested on Saturday in connection with the raid at what officers called a homemade laboratory in the industrial area of Tsuen Wan.
Police officials found 2 kg of the highly volatile triacetone triperoxide (TATP), 10 petrol bombs, acidic substances, knives and metal rods, gas masks as well as goggles, the South China Morning Post reported.
"It's the largest such seizure we have ever come across in Hong Kong," said Alick Mcwhirter, Superintendent of the Explosive Ordinance Disposal unit.
McWhirter said his squad handled about one kg TATP on Saturday and were working on another kg of explosives. The process was expected to take some time, he said.
TATP was used in deadly terrorist attacks, including the 2005 London bombing, the 2015 Paris attacks, the 2016 Brussels bombing, the 2017 Manchester bombing and a failed attempt by an Islamist in Brussels in 2017.
Also found in Tsuen Wan were banners and leaflets opposing the extradition bill and a T-shirt with logo of the pro-independence Hong Kong National Front group.
The arrested man is still being questioned. The Hong Kong National Front said in a post distributed on the Telegram app the man was a member of the group, but denied any knowledge of explosives.
Mass protests seeking government reforms and democracy have become a familiar sight in Hong Kong over the past six weeks, as hundreds of thousands of people have taken to the streets.
The demonstrations were initially sparked by public opposition to the extradition bill that would have allowed people in Hong Kong to be extradited to face trial in mainland China.
Though the bill has since been suspended, demonstrations have continued.
( With inputs from IANS )