Police in Hong Kong have discovered a stash of a powerful homemade explosive as the semi-autonomous Chinese city readied for another major pro-democracy protest on Sunday.

Key points: Protests against Hong Kong's Government have become increasingly violent

Protests against Hong Kong's Government have become increasingly violent Police claim to have made the largest-ever seizure of explosives

Police claim to have made the largest-ever seizure of explosives Pro-Beijing counter-protesters also turned out in force on Saturday

Police said they found about 2 kilograms of TATP and arrested a man in a raid on a commercial building late on Friday night.

TATP, or tri-acetone tri-peroxide, has been used in terrorist attacks worldwide.

Banners voicing opposition to an extradition bill that has sparked more than a month of demonstrations were found at the lab, according to police.

Police arrested a 27-year-old man and were investigating his possible links to a major protest planned for Sunday.

It is thought to be the largest quantity of explosives ever seized in Hong Kong. ( Apple Daily via AP )

"I think without a doubt this is the largest seizure we have ever come across in Hong Kong," said senior bomb disposal officer Alick McWhirter, as quoted by the South China Morning Post.

He said the homemade explosive was very unstable and extremely powerful. One kilogram was detonated on Saturday morning.

Other items seized from the factory included 10 petrol bombs, knives and metal rods. Police said more arrests may follow.

Authorities have erected huge barricades near government headquarters in preparation for Sunday's march.

Pro-police protesters carried red umbrellas and mainland Chinese flags. ( AP: Vincent Yu )

Earlier protests have often ended with police clashing with groups of protesters trying to occupy streets or refusing to disperse.

A counter-rally in support of the police was held on Saturday evening, with tens of thousands calling for an end to violence.

Some waved Chinese flags as others chanted "Hong Kong Cheer Up" and "Support Hong Kong Police".

Last weekend two initially peaceful protests degenerated into running skirmishes between baton-wielding riot police and activists, resulting in scores of injuries and more than 40 arrests.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 53 seconds 53 s Protesters injured after clashes with riot police in Hong Kong mall

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