Warning: Graphic and disturbing content
Dramatic video has caught a pro-Beijing man who stabbed a young Hong Kong protester in the neck and stomach waving his knife and yelling as the victim's friends begged for an ambulance.
The attack was so severe, the 19-year-old victim's intestines were exposed as he lay on the ground, reports News.com.au.
The attack took place in a subway station at Tai Po, in Hong Kong's New Territories, around 5.30pm on Saturday as the teenager handed out pro-democracy flyers ahead of Sunday's mass demonstration rally.
The assailant was taking down pro-democracy posters in the subway before he attacked the teenager.
"The man charged at him and slashed him in the neck. My friend ran away, and when he fell on the ground, the assailant stabbed him in the stomach," a witness told Radio Television Hong Kong.
After stabbing the 19-year-old, the assailant walked to a nearby bus terminal where he brandished the knife and hurled insults at the protesters.
Yelling in Chinese, he said: "Listen, you useless Hong Kong youth, Hong Kong is a part of China, and I will go against whoever disrupts Hong Kong".
With the teenager seriously wounded, the assailant then jumped in a taxi and escaped.
The victim had been distributing the pro-democracy flyers near Tai Po's Lennon Wall.
It is one of the largest of the Lennon Walls, the mosaic walls festooned with posters and messages which began cropping up in the first Umbrella Movement uprising in 2014.
In the video taken after the stabbing, the attacker punches the air and yells out with the knife still in his right hand.
Wearing black jeans and T-shirt with short black hair, the assailant appears to be aged in his twenties.
The voices of onlookers can be heard yelling back obscenities as vehicles drive by the attacker.
The wounded teenager was taken to Prince of Wales hospital in the New Territories.
Tai Po Police District Investigation team arrested a 22-year-old man on Saturday evening in connection with the case.
The Lennon Walls around greater Hong Kong have been the site of previous attacks.
In August, at the Lennon Wall in Tseung Kwan O in eastern Hong Kong, three people were wounded in a knife attack.
The Hong Kong protests began against the government's proposed extradition law amendment bill, which would allow it to extradite criminals to the jurisdiction of mainland China.
After the controversial bill was withdrawn, protesters continued to call for Hong Kong Chief Executive Carrie Lam to meet their demands including an inquiry into police brutality.
The Chinese government has described the protests as the "worst crisis" to befall Hong Kong since the independent territory was handed back to China in 1997.
China issued a warning in August they would not stand by and let "intolerable" dissidence continue and may intervene with troops.