A pro-democracy protester from Hong Kong was dragged into the Chinese consulate in Manchester on Sunday and beaten, according to a video released by the BBC.

Unidentified men came out of the consulate and chased the man into the compound before he escaped with the help of police and other protesters. The protester told the BBC: “They dragged me inside and beat me.”

A spokesman for the consulate said the protesters were displaying an offensive portrait of the Chinese president. Manchester police have launched an investigation.

Speaking after the incident, a protester surnamed Bob told BBC China that “mainlanders” – people from mainland China, not Hong Kong – came out of the consulate and destroyed their posters.

The crowd was enraged after the incident. Protesters chanted against the men outside the consulate and British police, saying they could have done more.

The British Prime Minister’s press secretary Liz Truss said on Monday that the apparent aggression was cause for concern, according to Reuters.

“This information is obviously deeply disturbing. I understand that Manchester Police responded immediately to the incident. I know their inquiries are ongoing, so it would be inappropriate for me to comment beyond that,” a media spokesperson said.