HONG KONG • Hong Kong police yesterday said they had uncovered a makeshift factory producing high-powered explosives alongside pro-independence leaflets, a discovery which comes as the city is rocked by unprecedented political protests.

The police said they swooped in on an industrial building in the district of Tsuen Wan on Friday evening and arrested a 27-year-old man.

"We are dealing with a homemade laboratory for the manufacture of explosives, specifically TATP (triacetone triperoxide)," Superintendent Alick McWhirter, a bomb squad specialist, told reporters.

"This is an extremely sensitive and an extremely powerful high explosive. It will cause exceptional amounts of damage when used," he added.

TATP requires skill to manufacture but has been used in a number of major terror attacks, including the 2005 London suicide bombings and the deadly Easter attacks on hotels and churches in Sri Lanka earlier this year.

Supt McWhirter said his team had carried out at least one controlled explosion and expected to do more because the TATP that had been discovered was volatile.

Items displayed by the police after the raid included a T-shirt with the logo of the Hong Kong National Front, a pro-independence group, as well as leaflets related to the anti-government protests currently engulfing the international finance hub.

The Hong Kong National Front, a small fringe group, released a statement on Facebook saying that the man arrested was a member but added it had no knowledge of any explosives.

In November 2017, two members of another fringe independent group were found guilty of making explosives and were jailed.

A small number of pro-independence groups have emerged but they remain fringe elements with little popular support.

AGENCE FRANCE-PRESSE