A prominent Beijing-supporting politician has been stabbed in the chest by a suspected pro-democracy activist during election campaigning in Hong Kong.

Junius Ho, an outspoken critic of the movement for greater civil freedoms and autonomy in the city, was attacked in the street by a man pretending to be his supporter.

It is the latest instance of tit-for-tat violence in Hong Kong’s months-long unrest. On Sunday night, a Mandarin-speaking Beijing supporter armed with a knife attacked a group of pro-democracy activists outside a mall, injuring several of them and biting off part of an opposition politician’s ear.

Mr Ho was being filmed when Wednesday’s attack took place. Video of the incident that is being circulated online shows a man dressed in blue and wearing a baseball cap approach the politician and offer him flowers.

The man then reaches for his bag, saying he wants to take a picture. Instead, he pulls out a knife and lunges at 57-year-old Mr Ho’s chest. The politician and others quickly wrestled the attacker to the ground.

The man continued to hurl abusive comments at Mr Ho as he was overpowered, calling him “human scum”.

Police said they had arrested one suspect and that three people injured in the incident, including Mr Ho, were receiving treatment and “conscious”.

In a statement posted online, Mr Ho said he had suffered a knife wound to the upper left part of his chest but said his life was not at risk.

He said that “black forces” were targeting pro-establishment candidates ahead of the district council elections taking place later this month. “I will remain courageous and fearless,” he said.

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Mr Ho received widespread media attention in July when he posed for photographs with white-shirted members of a pro-Beijing mob who had attacked democracy activists in a train station.

In the pictures, Mr Ho shook hands with the alleged triad members and gave a thumbs up.

He was accused at the time of orchestrating the train attack. Mr Ho said he had praised the men for “defending their home and people” but denied involvement in their actions, or knowledge of the violence.

After the train attack incident, Mr Ho’s office was attacked and his parents’ graves vandalised. The British university he attended, Anglia Ruskin, withdrew an honorary doctorate it had given him in 2011, saying the politician’s “conduct since he was honoured has caused increasing concern”.

Hong Kong’s government strongly condemned the attack on Mr Ho and said in a statement that members of the public should “express their views in a peaceful and rational manner with respect for each other”.

Protest leaders have also been targeted in attacks in recent months. Jimmy Sham, a leader of Hong Kong’s Civil Human Rights Front, was beaten by several men with hammers in October after his group organised some of the largest mass rallies against a deeply unpopular – and now withdrawn – extradition bill.

Meanwhile on Wednesday, a senior Chinese official said Beijing supported “more proactive and more effective measures” to solve the ongoing crisis.

Meeting with Hong Kong’s chief executive Carrie Lam in Beijing, China’s vice premier Han Zheng said the anti-government protests were damaging the principle of “one country, two systems” under which a number of Chinese special administrative regions are governed.

Mr Han said the violence had crossed what he called the “bottom line” of the rule of law and morality. His comments came after the Communist Party said on Tuesday that it would not tolerate “separatist behaviour” in Hong Kong, accusing some activists of calling for outright independence.