Hundreds of people took part in a peaceful sit-in on Monday night in Hong Kong to mark the anniversary of a violent attack on pro-democracy protesters by men wearing white shirts in Yuen Long MTR station, but the night ended with the streets full of tear gas as yet more clashes erupted between protesters and police.

Online calls earlier in the day had asked people to gather at the station at 7pm, but the MTR Corp closed it at 2pm.

At the adjacent Yoho shopping mall, about 100 protesters sat on the floor from 7pm on singing the protest song Glory to Hong Kong, despite the mall closing at 5pm. The sit-in was peaceful.

Tensions arose when a black-clad group that had been planning a sit-in at the station changed tactics and started blocking Castle Peak Road with barricades. Riot police quickly arrived and dispersed the crowd.

Police stopped and searched people on the streets and told bystanders to take off their masks or they would be arrested. Many residents in plain clothes gathered to confront the police. Some accused the police of blocking the roads, while others questioned them over their response to the July 21 attack. They chanted slogans, saying “disband the police force immediately.”

Then flash-mob protests happened in various areas in the district and barricades were set up to block the roads.

At about 9:30pm, police fired multiple rounds of tear gas in Kuk Ting Street, Tai Tong Road and near residential buildings in Hong Lok Road after a stand-off with angry residents, but no black-clad protesters were seen there.

At 10:30pm, some bystanders confronted police on Castle Peak Road. Riot police fired tear gas on the sidewalk and subdued at lease one bystander.

The police force later said in a social media post that the tear gas was used after “rioters” threw unspecified hard objects at police. They urged people to avoid the area and local residents to keep their windows closed and to stay indoors.

The “indiscriminate and violent attack” that happened three months ago ignited a storm of protest against the Hong Kong police force. A political storm had erupted in the city by that time after the Hong Kong government had proposed an amendment to the extradition bill in June.

On July 21, more than 100 men dressed in white and armed with rattan sticks and steel poles launched a brutal attack on pro-democracy protesters, train passengers and reporters at the Yuen Long MTR station, leaving almost 50 people injured.

The attack was broadcast live on social media and shocked tens of thousands of Hong Kong people.

The police were heavily criticized for taking 39 minutes to reach the station, despite frantic calls from citizens who were attacked, and they failed to arrest any of the armed assailants on the spot. The media filmed the men in white wielding rattan sticks and steel poles, while the riot police stood aside.

Later there were allegations that the police had colluded with triad organizations because media reports showed police releasing the suspected gangsters after the attacks.

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One of the protesters who joined the three-month anniversary sit-in said he simply could not accept a call last week made by chief secretary Matthew Cheung Kin-chung for people to “move on” from the July 21 attack and wait for a report from the Independent Police Complaints Council, Radio Television Hong Kong reported.

“We can’t forget this, because I think that this is so horrible to all Hong Kong people and this should not be moved on from until the criminals are caught and in the jails,” the secondary school student said.

A Yuen Long resident surnamed Ho agreed, slamming Cheung’s “move on” comment, saying it was ridiculous and humiliating to Hong Kong people.

Ho slammed the police for their unfair handling of the suspects as they only laid charges on six suspects among the 34 they arrested. But with the arrested protesters, police quickly pushed them into court on charges, even though they suffered injuries during the protests.

One of those injured during the July 21 attack, a cook surnamed So, said the police only took a statement from him once and there had been no further process since then, the Apple Daily reported. So said he had checked with police, but was told they had not arrested the suspects who had beaten him up on the street.

So was off-duty that night. As he was wearing a black T-shirt, the color the pro-democracy protesters use, he was chased after and hit by about 20 white-clad men with rattan sticks. His suffered a serious injury to his back and needed a month to recover.

So was injured by about 20 white-clad men in Yuen Long. Photo: Facebook

Police arrested 34 men aged 18 to 60 for being involved in the Yeun Long attack on July 21, six of whom have been prosecuted for rioting.

“We have been following the case actively. If we have sufficient evidence, we will consult the Department of Justice and press charges,” said Li Kwai-wah, a senior superintendent of the anti-triad bureau, during the police press conference on Monday.

People in several other districts also staged rallies to commemorate the attack in July.

About 100 people held a sit-in and chanted slogans at Tuen Mun MTR Station, and others at Tai Koo and Tseung Kwan O stations demanded the MTR release surveillance camera footage of the attack three months ago.