A brutal attack by masked men on pro-democracy protesters at a train station in Hong Kong was an attempt by the city’s pro-Beijing elements to “silence the voice of Hong Kong’s people”, says activist leader Joshua Wong.

Outrage grew in the city as more details emerged of what appeared to be a coordinated assault by dozens of men, dressed in white T-shirts and armed with metal and wooden poles, who stormed the Yuen Long metro station hours after the end of a largely peaceful protest march.

Videos showed groups of men in white rushing through the station concourse and appearing to target those dressed in black, the colour of the protest movement. Ordinary commuters were caught up in the violence, and at one point were forced to flee back on to a train as the attackers swarmed the platform.

Speaking to The Independent, Mr Wong said the unprecedented attack was the work of members of Hong Kong’s organised crime triads, apparently “engaged and coordinated” by those who support the rule of mainland China. Some members of the mob were photographed smiling and shaking hands with the pro-Beijing politician Junius Ho, he said.

Among some 45 people injured in the attack were the pro-democracy politician Lam Cheuk-ting, who was repeatedly struck in the face, and the news reporter Gwyneth Ho, who was live-streaming the incident for Stand News when she was beaten. At least 15 remained in hospital as of late Monday evening.

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Anti-extradition protesters broke into the the city's legislature and thousands more gathered to march in opposition to the city's China-backed government during the 22nd anniversary of Hong Kongs return to Chinese rule Getty Turbulent protests continue in Hong Kong: In pictures Police fire tear gas at protesters near the government headquarters AFP/Getty Turbulent protests continue in Hong Kong: In pictures A protester defaces the Hong Kong emblem AFP/Getty Turbulent protests continue in Hong Kong: In pictures Protesters try to break into the Legislative Council of Hong Kong during a protest on the 22nd anniversary of the handover of the territory to China from Britain on July 1 Reuters Turbulent protests continue in Hong Kong: In pictures Black-clad riot police fired tear gas as they charged anti-government protesters in the early hours of the morning AFP/Getty Turbulent protests continue in Hong Kong: In pictures A general view of the main chamber after protesters break into the Legislative Council building EPA Turbulent protests continue in Hong Kong: In pictures Protesters graffiti the Legislative Council Complex Getty Turbulent protests continue in Hong Kong: In pictures Police fire tear gas at protesters near the government headquarters in Hong Kong on July 2, 2019. - Riot police fired tear gas as they attempted to dislodge anti-government protesters in the early hours of the morning of July 2 in chaotic scenes in the heart of Hong Kong. (Photo by Anthony WALLACE / AFP)ANTHONY WALLACE/AFP/Getty Images ANTHONY WALLACE AFP/Getty Turbulent protests continue in Hong Kong: In pictures Inside the Legislative Council building EPA Turbulent protests continue in Hong Kong: In pictures Protesters put up a sign AFP/Getty Turbulent protests continue in Hong Kong: In pictures Members of the press take pictures of a protest banner that says 'there are no violent people, only violent governance' EPA Turbulent protests continue in Hong Kong: In pictures Protesters storm the Legislative Council building during a protest in Hong Kong on July 1 Reuters Turbulent protests continue in Hong Kong: In pictures A protester forces their way through a window into the Legislative Council building in Hong Kong on July 1 Reuters Turbulent protests continue in Hong Kong: In pictures Police officers look out from behind windows damaged by protesters in the entrance to the Legislative Council in Hong on July 1 AFP/Getty Turbulent protests continue in Hong Kong: In pictures Police officers stand guard behind the entrance to the Legislative Council in Hong Kong as protesters try to force entry. One officer holds a sign that reads: "Stop charging or we use force" EPA Turbulent protests continue in Hong Kong: In pictures Protesters storm the Legislative Council building during a protest in Hong Kong on July 1 Reuters Turbulent protests continue in Hong Kong: In pictures Protesters wield makeshift shields during a clash with police on the 22nd anniversary of the territory's handover to China from Britain on July 1 Getty Turbulent protests continue in Hong Kong: In pictures Protesters holding umbrellas face-off against riot police in Hong Kong on July 1 AP Turbulent protests continue in Hong Kong: In pictures Protesters smash a window of the Legislative Council building in Hong Kong on July 1 AFP/Getty Turbulent protests continue in Hong Kong: In pictures A protester wielding a makeshift shield looks back at the damage caused to the Legislative Council building in Hong Kong on July 1 Reuters Turbulent protests continue in Hong Kong: In pictures Protesters gather to take part in the annual pro-democracy rally that is held in Hong Kong on the anniversary of the handover of the territory from Britain to China on July 1 AFP/Getty Turbulent protests continue in Hong Kong: In pictures Police officers use force in an attempt to disperse protesters during a protest in Hong Kong on the 22nd anniversary of the handover of the territory from Britain to China on July 1 Reuters Turbulent protests continue in Hong Kong: In pictures Anti-extradition bill protesters stand behind a barricade near the Legislative Council of Hong Kong on July 1 Reuters Turbulent protests continue in Hong Kong: In pictures Police officers look out from behind windows damaged by protesters in the entrance to the Legislative Council in Hong on July 1 AFP/Getty Turbulent protests continue in Hong Kong: In pictures Protesters try to break into the Legislative Council of Hong Kong during a protest on the 22nd anniversary of the handover of the territory to China from Britain on July 1 Reuters Turbulent protests continue in Hong Kong: In pictures Protesters rest outside the Legislative Council in Hong Kong on July 1 EPA Turbulent protests continue in Hong Kong: In pictures A protester shouts in front of police outside the Legislative Council in Hong Kong on July 1 AFP/Getty Turbulent protests continue in Hong Kong: In pictures A group of anti-extradition bill protesters holding umbrellas gather outside the government headquarters in Hong Kong on July 1 AFP/Getty Turbulent protests continue in Hong Kong: In pictures A protester waves a black version of the Hong Kong flag outside of the Legislative Council of Hong Kong on July 1 Getty Turbulent protests continue in Hong Kong: In pictures Anti-extradition bill protesters march in Hong Kong on the anniversary of the territory's handover to China on July 1 Reuters

Carrie Lam, Hong Kong’s chief executive, called the scenes “shocking” and urged for calm on all sides, saying that “violence will only breed more violence”. She also condemned protesters who clashed with police earlier in the day and defaced China’s main representative office in the city.

But while Ms Lam said police would investigate the events at Yuen Long, and two alleged mob members were arrested on Monday, questions were already being asked about why it took officers up to an hour to intervene and stop the train station assault.

Mr Wong said Hong Kong police chief Stephen Lo’s claim that officers had to wait for backup from other districts was a “misleading excuse”.

“Gangsters serving the interests of Beijing physically attacked not only protesters but also pregnant women, the elderly and children,” he said. “When people dialled the emergency 999 hotline, police just hung up the phone. They had 1,000 officers at the nearest station but did not send anybody.”

Mr Wong, who was repeatedly arrested for his involvement in the 2014 Umbrella Movement protests, said Hong Kong’s pro-Beijing camp had used hired thugs before to target mass demonstrations – but never to beat up “ordinary citizens” going about their business in the city.

“The pro-Beijing camp must realise that they go too far [this time], that this will just trigger more ordinary Hong Kong citizens [to] stand on the side of protesters.”

Formally, police are still investigating who carried out Sunday night’s assault. Yau Nai-keung, an assistant police commander in the area, defended the lack of arrests, saying: “We can’t say you have a problem because you are dressed in white and we have to arrest you.”

Mr Lam, the politician caught up in the violence, said he was sure it was the work of triads, and that he personally made repeated calls to the police which were ignored.

“They deliberately turned a blind eye to these attacks by triads on regular citizens,” he said, describing how the floors of the station were streaked with blood.

“I won’t speculate on why they didn’t help immediately,” he said.

The shocking scenes of Sunday night were only the latest episode in Hong Kong’s worst political crisis since the 1997 handover of power from Britain to China.

Since the start of the year, protests that began in uproar against a new extradition bill have snowballed into a mass show of defiance towards Beijing and the “one country, two systems” principle under which Hong Kong is ruled.

Ms Lam and the city’s government have already said the extradition bill is “dead” in this legislative term and will not be revived unless and until it receives popular support, but protesters are demanding its full withdrawal, plus Ms Lam’s resignation and a promise of amnesty from prosecution for those who have taken part in demonstrations.

Protests have taken place each weekend for the past two months, and on Sunday police again fired rubber bullets and tear gas to disperse activists after thousands had rung Beijing’s Liaison Office. Protesters had spray-painted and egged the walls and a Chinese national emblem outside the building.

The choice of the office as a target has struck a nerve on the mainland. The Chinese government, including office director Wang Zhimin, said the development challenged the “authority and dignity” of China.

Geng Shuang, a foreign ministry spokesperson, said the “radical protestor behaviour” had tested Beijing’s limits, adding: “We cannot tolerate that.”

The protesters’ actions were condemned in the official People’s Daily newspaper, in a front-page commentary headlined “Central Authority Cannot Be Challenged”.

And Ms Lam warned the vandalism had “hurt the nation’s feelings”.

The growing crisis has given rise to fears that China might consider a military intervention. On Monday, a social media statement from a Chinese army brigade said it had held an “anti-terrorism” exercise in southern Guangdong province, which borders Hong Kong.

That statement did not refer to Hong Kong directly, but military commentator and retired officer Yue Gang said that troops would be dispatched to the territory if needed.

“To deface the Chinese national emblem is like acting as an enemy to 1.3 billion Chinese people,” Yue told the Associated Press. “They must be deterred.”

The next protests would continue as planned on Saturday and Sunday despite the attack, Mr Wong said, and would continue “every weekend… to show the people have the power”.