British Prime Minister Liz Truss expressed “deep concerns” on Monday after a video emerged that appeared to show a Hong Kong activist being beaten inside the Chinese consulate in Manchester during a protest, as local police launched an investigation into the incident.

Video footage circulating online showed a man was apparently pulled inside the grounds of the consulate and beaten by a group of unidentified men.

The victim was among protesters on Sunday who gathered in front of the Chinese consulate in Manchester, with the group setting up two banners featuring slogans with foul language directed at the opening of the Chinese Communist Party’s twice-in-a-decade congress in Beijing.

A spokesman for Truss said reports of the incident were “obviously deeply concerning”.

“I understand Greater Manchester Police responded immediately to the incident. I am conscious that their inquiries are ongoing so it would be inappropriate for me to comment beyond that,” he told the Post in a statement.

A minute-long video also showed a brawl erupting as a grey-haired man in a blue scarf, who appeared to have come out of the consulate, went to tear down one of the banners before going back to the consulate.

At the same time, a scuffle seemed to erupt at the front gate of the consulate. Police officers quickly stepped in and pulled away the protesters and stopped them from getting near.

British Prime Minister Liz Truss.

The Greater Manchester Police said an investigation had been launched, and it understood the “shock and concern” the incident had caused. It was liaising with national law enforcement and diplomatic partners, the force added.

“A full and comprehensive investigation is under way by our experienced Major Incident Team detectives, and I can assure the public that all viable avenues will be explored to bring to justice anyone we believe is culpable for the scenes we saw outside the Chinese consulate on Sunday,” said Rob Potts, the regional force’s assistant chief constable.

The alleged victim, who identified himself as a Hongkonger named Bob, said in a Cantonese interview with the BBC: “Some mainlanders came out and destroyed our things. When we tried to stop them I was pulled inside and beaten up. Then I was dragged out by several policemen.

“It was totally unreasonable. They should not have done so. I have freedom of expression,” he said. “We protested peacefully. Why should we deserve to be beaten up?”

A spokesman for the Chinese consulate in Manchester earlier told the British public broadcaster the protesters had “hung an insulting portrait of the Chinese president at the main entrance”.

“This would be intolerable and unacceptable for any diplomatic and consular missions of any country. Therefore, we condemn this deplorable act with strong indignation and firm opposition,” he said.

The Post has reached out to the consulate for comment.

Regarding the incident on Sunday, Greater Manchester Police said their officers had decided to intervene and remove the alleged victim from the consulate grounds over fears for his safety. The force said he was dragged by a small group of men who came out of the building into the consulate area and assaulted him.

The victim, who is in his 30s, suffered several injuries and remained in hospital overnight for treatment, the force said, adding no arrests had been made so far.

A screengrab of footage from October 16 showing protesters gathering outside the Chinese consulate in Manchester.

British politician Iain Duncan Smith, of the Conservative Party, said the British government “must demand a full apology from the Chinese ambassador to the UK Zheng Zeguang and demand those responsible be sent home to China”.

Catherine West, a Labour member of Parliament, took to social media to describe the incident as “deeply concerning”, pledging to raise the issue with the government.

Fugitive and former Hong Kong lawmaker Nathan Law Kwun-chung called on the country’s foreign and home secretaries to investigate the issue and “protect our community and people in the UK”.

“If the consulate staff responsible are not held accountable, Hongkongers would live in fear of being kidnapped and persecuted,” Law wrote on social media.

Hong Kong activists’ groups in the United Kingdom also issued a joint statement, asking the British government to investigate “the violation of international law”.

Sunday’s protest was organised by a pro-Hong Kong independence group in Britain, Hong Kong Indigenous Defence Force, which had meant to “surround” the consulate to voice their opposition to the Beijing government and the opening of the Chinese Communist Party’s congress, according to a Facebook post from the group last week.

They appealed to supporters to join and “do something that cannot be done in Hong Kong” and hoped their voice could spread to the international community via the media.