Hong Kong (CNN) Police in Hong Kong have seized what is thought to be the largest ever cache of high-powered explosives uncovered in the city, in a raid Friday night on a suspected bomb-making factory.

The discovery comes on the eve of a series of high-profile protests planned over the weekend, amid high tensions in the semi-autonomous Chinese city over a now-suspended extradition bill.

Police have confirmed the arrests of three local men aged between 25 and 27 in connection with the raid at what officers called a homemade laboratory in the industrial area of Tsuen Wan.

Police uncovered 2 kilograms (4.4 pounds) of high explosives, 10 petrol bombs, corrosive liquids, weapons and metal poles at the property.

The discovery comes on the eve of a series of high-profile protests planned over the weekend.

"It's the largest such seizure we have ever come across in Hong Kong," said Alick Mcwhirter, superintendent of the Explosive Ordinance Disposal (EOD) Bureau. Leaflets linked to anti-extradition bill protests were also found on site.

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