At least 29 protesters were fined HK$2,000 each for breaching the social gathering ban while two others were arrested for allegedly possessing weapons as two malls in Mong Kok erupted with flash mob chanting and singing on the eve of the August 31 incident.
The confrontation saw 150 police officers rushing into Moko mall and Langham Place where at least 100 black-clad people protested over the August 31, 2019, incident in which police battered and pepper-sprayed protesters and commuters inside the Prince Edward MTR station, leading to accusations of indiscriminate police violence.
A 16-year-old boy was arrested in Mong Kok MTR station for possessing an imitation pistol and a 39-year-old man was nabbed outside Langham Place for having an extendable baton in his bag.
As of 8pm, nine men and five women were fined in Moko mall, and 13 men and two women slapped with the fixed penalty in Langham Place.
The standoff began at around 2pm, with protesters gathering in Moko mall and hundreds of police officers arriving around 3.30pm.
Police warned protesters that shouting the slogan "Liberate Hong Kong, revolution of our times" could violate the national security law.
Protesters subsequently went to Langham Place around 4pm, with officers searching any residents who entered the mall. At least one man was taken away after being stopped.
Police entered the mall half an hour after protesters left and began to fine anyone caught breaching the social gathering ban, with two males and a female fined during the evening.
Yesterday's protests follow the assault of three men and a woman after a dispute in front of a "Lennon Wall" in Sheung Shui late Saturday night.
A group of people tried to tear down materials at the site near the North district town hall, according to the district council chairman, Jasper Law Ting-tak.
A man tried to stop them, at which point the group attacked him and others who came to his aid. A man was hit in the head with a glass bottle, with the gang fleeing the scene.
Three men and a woman, aged 30 to 56, were treated at North District Hospital, with one person in serious condition transferred to Prince of Wales Hospital in Sha Tin.
A video shows two men started punching a teenager, while another man sitting on the floor beside him was soaked in blood.
The two assailants then left with around eight other people and warned witnesses not to follow them.
Meanwhile, a 40-year-old man was arrested for criminal damage in North Point MTR station yesterday after he wrote phrases related to the August 31 incident on a wall.