The actions were just one of many throughout the evening that began in Mong Kok. Protesters surrounded Mong Kok Police Station and stood outside Prince Edward MTR station from late afternoon. At around 7pm police dispensed tear gas and pepper spray as protesters hurled water bottles at police wagons and threw bricks prised from the pavements to obstruct traffic.

They also vandalised traffic lights and exits of Mong Kok MTR station, forcing the station to close, before starting a fire on Nathan Road at about 9pm.

During the police operation in Central, a man RTHK identified as one of its video journalists was hit with pepper spray by police after he asked officers to show him their identification numbers.

A spokesman for the broadcaster said the reporter was wearing a vest with its logo clearly displayed. He said reporters had been injured by officers’ “unnecessary force” while carrying out their work, and had also been obstructed by police.

“[RTHK] expresses anger and issues a reprimand,” the broadcaster said in a statement, and urged police to respect press freedom.

The Hospital Authority said six people were injured on Thursday night, including one who was in a serious condition.

Meanwhile, the Social Workers’ General Union claimed one of its members was hit on the head by a police officer in Prince Edward. The union claimed as the social worker was being taken to an ambulance an officer said: “Do you know how you got injured? Are you sure you did not just fall?”

On Hong Kong Island, about 100 people, most with their faces covered, started to gather at Victoria Park in Causeway Bay at 7pm for an unauthorised march to Lan Kwai Fong to protest against a government ban on wearing masks at public assemblies.

Marchers wore all kinds of disguises, ranging from Halloween masks to paper cutouts of political figures and fictional characters.

Office worker Kenny Chum, in his 30s, wore a mask of US President Donald Trump. He said he wanted to use this festive occasion to protest against the anti-mask law and police’s use of force.

“I feel it’s a day where it’s fine to wear face mask, like all Halloweens in the past,” he said.

“Police are overly sensitive and have made things feel tense. It’s supposed to be a day for fun.”

Loo Lo, 25, said she always celebrated Halloween but there was a political side to this year. She dressed as the Joker, a character she said symbolised the fight against the government and the anti-mask law.

“We could all be the Joker and we are connected, to fight the same cause,” she said.

Earlier in the day, streets in the bar district had been barricaded with water barriers for the first time and about 30 police officers in full riot gear were seen on Wyndham Street in Central.

They were among 3,000 officers expected to be mobilised on Thursday night, while three water cannons were also stationed on Hong Kong Island.

The Lan Kwai Fong Association, a business body composed of about 100 restaurants and service providers in the area, hired marshals to set up the barriers from 4pm. Shopkeepers and restaurant workers said it was the first time such barricades had been used.

The marshals refused to allow people without party passes or bookings to pass through.

Police sources said Halloween party-goers could be forced to wipe off face paint if they looked suspicious, while undercover officers would blend into crowds during the planned march from Victoria Park in Causeway Bay to Central.

At Tipsy Bird bar in Lan Kwai Fong, an employee called Alex Batthaly, 35, said sales so far were down between 35 and 40 per cent year on year.

“It’s so quiet,” he said, adding it was the worst business he had seen for the bar in his three years working there.

Frankie Chan, a food and beverage business developer, also said business had been difficult in the past few months.

“I’ve been operating restaurants in Lan Kwai Fong for nearly three decades. This year, I had no choice but to shut down three of my stores in the area,” he said.

Among the revellers in Lan Kwai Fong was Wing Siu, 36, who works as a personal life coach.

Siu came to the nightlife district with his two-year-old son who had his face painted like a clown. He said the festive atmosphere was quieter in the entertainment area compared with last year and admitted there were safety risks.

“We will just take good care of ourselves,” he said. “We still have to eat and live anyway.”

Peter Law, 26, wore a mask featured in V for Vendetta. The engineer said he had not celebrated Halloween in previous years, but this year wanted to express his dissatisfaction over the anti-mask law. He insisted he was not taking part in a public assembly, but to celebrate the festival.

“If police arrest people celebrating, then I have nothing to say. It only proves Hong Kong is a police state.”

In Lan Kwai Fong, most bars were opened as usual, but even those on the main road were not full or busy.

Nevertheless, police blocked the junction between D’Aguilar Street and Wellington Street at 8pm, causing a stand-off between officers and hundreds of residents.

Waqas, a bartender at a bar called Chocolate, said the police presence had made business worse.

“If police weren’t here, at least some of our regular guests would have come for a drink,” he said.

Sahil Md, 33, an employee at two bars at Win Wah Lane, said police blocking the entrances meant no businesses for them.

He recalled the two stores made about HK$120,000 this time last year, but the figure had dropped 90 per cent in 2019.

Earlier in the evening, residents gathered outside Prince Edward MTR station in Mong Kok to denounce alleged police brutality.

Police and protesters clashed inside the station on August 31, leading to a number of injuries. When the number of people hurt was revised, rumours circulated that some protesters had died in the station, prompting the disciplined services to issue several statements clarifying the situation.

The station was shut at 2pm on Thursday, while Mong Kok station was closed at 8pm out of safety concerns. Rail operator MTR Corporation also said Central station would be shut at 9pm.

The entire MTR network, except for the Airport Express, shut down at 11pm and the MTR Corp warned that individual stations or entrances could close at any time depending on further risk assessment or whether protesters damaged facilities.

A woman, who only gave her surname Ng, was seen limping to find an entrance at Prince Edward MTR station just before 2pm. She said she had just seen a doctor about a torn ligament and complained that the MTR had closed the entrance she usually used.

More than 100 people gathered around a “Lennon Wall” outside the station from 5pm, chanting slogans associated with the protest movement. They called again for the release of CCTV footage during the police action on August 31.

University student Chan Pak-san, 24, who was replacing a flower on the wall at the station said: “I come here regularly to protect this place and to preserve the memory of what happened on [August] 31. I hope the citizens of Hong Kong will remember what happened. We need to support the movement.”

A secretary, who gave her surname Tsoi, said she was hit by tear gas when she finished dinner in Mong Kok with her boyfriend.

“I walked out of the restaurant and saw this crowd. So I walked over to see and immediately police fired tear gas,” she said.

“What if people are just passers-by. This is unreasonable.” She called for the police force to be disbanded because she said they had been acting above the law.

On Lockhart Road in Wan Chai, bars and restaurants were open as usual, with reduced footfall compared with normal happy-hour time.

Angelo Ocambo, a bartender at a restaurant there, said sales in October fell between 20 and 30 per cent year on year. He recalled there was a continuous flow of customers from 4pm last Halloween, but this year diners only started coming in at around 5.45pm.

“It’s quite unusual for this time of the year,” he said.

Meanwhile, pro-democracy activist Ventus Lau Wing-hong’s appeal to overturn a police ban on a rally at Victoria Park on Saturday night was shot down on Thursday evening.

Lau said people could also attend two rallies in Chater Garden and Edinburgh Place on Saturday evening, which had been approved by police.

At midnight, a police source said at least 30 people were arrested in Central and Mong Kok.

Reporting by Martin Choi, Kathleen Magramo, Kanis Leung , Sum Lok-kei, Alvin Lum, Chris Lau and Tony Cheung