The ugliest incident, recorded on a video that went viral online, showed an unarmed man dressed in a blue shirt and trousers being attacked by a mob of black-clad masked protesters.

It was said to have occurred at about 4.30pm on Gloucester Road, near the junction of Marsh Road in Wan Chai. The man was reported to have confronted the protesters before he was attacked.

In the video, at least six protesters can be seen kicking him in the chest and back, punching his back and hitting him with umbrellas.

The man is seen shouting out and kneeling down, as if in surrender, covering his head with his hands. But his attackers continue raining blows on him, cheered on by others who clap their hands.

At one point, the man appeared to lose consciousness and was seen lying on the ground. A bag he had been holding was taken away. Separate television news footage showed him bleeding from the mouth.

The Hospital Authority later reported that a 49-year-old man was sent to Ruttonjee Hospital for treatment. Police sources confirmed that he was the victim on Gloucester Road. He was said to be in a serious condition.

There were more scenes of violence on Sunday night.

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A group of middle-aged men, some in white shirts, were seen holding a folding stool and a sledgehammer both outside and inside Fortress Hill MTR station. Some chanted, “Fujian people, beat the cockroaches! Go police!”, using a derogatory term for protesters. In one incident, a group was seen punching a black-clad man, who was crouching and protecting his head, inside the MTR station. One man was also seen hitting the head of a protester from behind.

Near North Point MTR station, a man wearing white was seen lying on the ground with his head bleeding. On the pavement near him sat another man dressed in white, bleeding from the mouth. When approached by reporters, he said he did not understand Cantonese.

A number of journalists, including a Post video producer, also became targets while covering the violence in North Point. One Post photographer was also punched in the face.

At around 8.20pm, near the junction of North Point Road and Chun Yeung Street, a group of unmasked men confronted journalists and abused them. Some in the group were wearing white T-shirts, and one tried to push the journalists away.

Riot police stepped in separate them from the journalists. A male journalist shouted at a police officer, demanding they arrest a man who he claimed had attacked a member of the press.

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Also in North Point, three men were seen on the street with butcher’s knives and they then kicked over two cans of what witnesses said smelled like flammable liquid. Police arrived within minutes but the men had locked themselves in the office of a group called the Hong Kong First Youth Association on Ming Yuen Western Street. Police eventually took seven people away from the building.

In August, some people had also been seen darting into the office after they fought with protesters using poles.

On Saturday, pro-Beijing groups gathered to sing the Chinese anthem and wave national flags at a rally in Amoy Plaza shopping centre in Kowloon Bay, after cleaning up a so-called “Lennon Wall” of stickers put up earlier by protesters.

Black-clad protesters confronted the pro-government individuals and, as tempers rose, arguments and fights broke out.