LONDON (AP) — British police said Monday they were investigating the assault of a Hong Kong pro-democracy protester who was beaten up on the grounds of the Chinese consulate in the city of Manchester.

The man, who is in his 30s, told the BBC that unidentified Chinese men from the consulate building dragged him inside the consulate and assaulted him during a protest on Sunday.

Greater Manchester Police said its officers intervened and removed the protester from the consulate grounds “due to our fears for the safety of the man.”

“Around 30 to 40 people gathered outside the Chinese Consulate, and local patrols were in the area to help maintain the peaceful protest,” police said. “Shortly before 4 p.m., a small group of men came out of the building and a man was dragged into the consulate grounds and assaulted.”

The protester remained in the hospital Monday for treatment, police said. No arrests have yet been made.

Video on the BBC website showed a scuffle breaking out in front of the consulate after masked men tore down and took away the protesters’ placards. The video appeared to show several men wearing face masks beating up someone who had been pushed to the ground amid the scuffles.

Downing Street said the incident was “deeply concerning,” adding that police had stepped up patrols in the area.

The Chinese consulate in Manchester did not immediately respond to requests for comment.

Andy Burnham, the mayor of Greater Manchester, said it was important for the full facts to be established, but added: “On the basis of what I have seen, I want to make clear that it is never acceptable for peaceful protesters to be assaulted and those responsible need to be held to account for their actions.”

The opposition Labour Party’s foreign affairs spokesman, David Lammy, called on the Conservative government to summon the Chinese ambassador to explain what happened.

The protesters had gathered as the Chinese Communist Party opened its weeklong congress in China on Sunday.