Hong Kong's security chief says some police officers who were captured on video kicking a democracy protester during an operation to clear demonstrators from a tunnel have been reassigned.

Secretary for Security Lai Tung-kwok said Wednesday that the officers were moved to other posts and that the police department is carrying out an investigation.

Local television channel TVB showed footage of around six plainclothes police officers taking a man around the side of a building, placing him on the ground and kicking him.

Police moved in to remove protesters and after they set up barricades in the tunnel in the dead of night. The clashes were the worst violence since the street demonstrations for greater democracy began more than two weeks ago.