[Graphic images] Hong Kong police made mass arrests on the streets of Causeway Bay on Sunday night – aided by men who appeared to be undercover officers dressed as protesters.

Photo: Holmes Chan/HKFP.

A protester was seen being wrestled to the ground by two men at around 10pm – one was a police officer in riot gear, the other was dressed as a pro-democracy protester in a yellow hardhat. In video footage captured by HKFP, the bloodied protester was seen moaning in pain and saying that his front tooth had been knocked out.

Photo: Holmes Chan/HKFP.

“I understand, don’t press me, I’m sorry,” he said as he was pinned to the ground. “I’ve already been arrested by you, I understand… Don’t do this, I beg you.”

Men dressed as protesters help police make arrests. Photo: Holmes Chan/HKFP.

Police officers were seen kicking the protester as he lay on the ground, his face pressed against a pool of his blood.

Men dressed as protesters help police make arrests. Photo: Holmes Chan/HKFP.

The man demanded a lawyer and repeated that he was complying with police.

Photo: Holmes Chan/HKFP.

The arrest came after fights reportedly broke out in the area between people dressed as protesters. Soon after, riot police charged at the group who were gathered at the intersection of Percival Street and Hennessy Road – a short distance away from the Sogo department store and Times Square.

Men dressed as protesters help police make arrests. Photo: Holmes Chan/HKFP.

Some men dressed as protesters aided riot police in subduing protesters: they brandished batons and wore respirators, despite no tear gas being fired in the vicinity of Causeway Bay. The police operation was conducted without warning, and many of the protesters were gathered on the street peacefully.

Photo: Holmes Chan/HKFP.

After police conducted arrests, the suspected undercover officers refused to answer questions from reporters. One man told a reporter to “use your professional knowledge,” but refused to confirm if he was a police officer.

Photo: Holmes Chan/HKFP.

Some of the suspected undercover officers carried green glow-sticks, which were used to signal their affiliation.

Men dressed as protesters help police make arrests. Photo: Holmes Chan/HKFP.

In HKFP’s video, the man who assisted in the arrest of the bleeding protester was also heard saying: “I’m on your side, I’m on your side.”

Photo: Holmes Chan/HKFP.

The incident could be the first proof of officers going undercover as protesters since the anti-extradition bill movement began in June.

Men dressed as protesters help police make arrests. Photo: Holmes Chan/HKFP.

On June 27, protesters who were surrounding the police headquarters in Wan Chai saw a man sprinting through the crowd with a windshield wiper. The man was later confirmed to be a plainclothes policeman, though police at the time denied any attempt to impersonate protesters.

Men dressed as protesters help police make arrests. Photo: Holmes Chan/HKFP.

“Police emphasises that the officer has neither disguised as a protestor nor made any incitement,” a Facebook statement read at the time. “Police [express its] utmost regret over the intentional spread of rumours and castigates the rumourmongers.”

Photo: Holmes Chan/HKFP.

The arrests in Causeway Bay took place as Hong Kong saw its tenth consecutive week of social unrest. Protesters defied police bans throughout Sunday, descending on multiple districts, with scores of people arrested in police clearance operations. Clashes erupted on Sunday among thick plumes of tear gas as riot police pushed protesters back in Sham Shui Po, Tai Koo, Cheung Sha Wan, Kwai Chung and Tsim Sha Tsui.

The city has been roiled by over two months of protests related to a now-suspended extradition bill. Anger over police conduct and calls for genuine democracy have escalated with neither the government nor protesters showing signs of compromise.