In a letter to the Civil Human Rights Front (CHRF) on Thursday, police said they feared some participants would commit “violent and destructive acts”.

Protesters have not only carried out “arson and large scale road blockades but also used petrol bombs, steel balls, bricks, long spears, metal poles, as well as various self-made weapons to destroy public property on a large scale, damage social order and cause injury to others,“ the letter said of previous protests, AFP reported.

The rare move comes after officers deployed water cannon and fired a warning gunshot to fend off radical protesters on Sunday night, after a sanctioned rally turned ugly.

Saturday’s rally was set to mark five years since Beijing rejected political reforms in Hong Kong, a decision which sparked the 79-day Umbrella Movement.

The CHRF, responsible for the largest rallies the city has seen in decades, said they would appeal the decision.

“You can see the police’s course of action is intensifying, and you can see (Hong Kong leader) Carrie Lam has in fact no intention to let Hong Kong return to peace, but is trying to incite the anger of more citizens through tough measures,“ the group’s leader Jimmy Sham told reporters.

Supporters had been urged to gather in the city centre and later march to the Liaison Office, the department that represents China’s central government in Hong Kong, but both aspects, which need permission from authorities, have been banned.

The last event organized by the CHRF on August 17 brought hundreds of thousands of people to the streets in a deliberate show of peaceful protest that saw demonstrators disperse without clashes.

On that occasion, the initial rally in a Hong Kong park was approved by authorities but protesters later defied a ban to march through the city.

The protests were ignited when the city’s Beijing-backed government tried to pass a bill allowing extraditions to mainland China, but have evolved into a wider call for greater democracy and an investigation into allegations of police brutality.

The mainly young protesters say their freedoms, unique within China, are being eroded by Beijing.

More than 850 people have been arrested since June.

The unrest has shown no sign of abating, with protesters locked in a stalemate with the Hong Kong government, which has refused to give in to their demands.