Wong was later arrested on suspicion of assaulting police officers and of resisting arrest. He "repeatedly hit an officer's face" with his video camera, police said before releasing the man on bail.

The case adds to growing discontent with the police's forceful clearance of the occupied Mong Kok site since Tuesday.

A senior police officer, believed to be a superintendent, will face an internal investigation after a video showed he used a baton to hit a man who later said he was "just a passer-by".

Yesterday, Amnesty International accused the police of being heavy-handed and "using unreasonable force to dispel protesters, journalists, onlookers and passers-by". The police's actions breached citizens' rights, it said.

The treatment of Wong, meanwhile, has riled journalists' groups. He is the second journalist in three days to be arrested in Mong Kok. A Now TV engineer was detained on the first day.

The Press Photographers Association voiced "extreme anger and regret". It said: "Police have once again threatened reporters by means of arresting them."

The Journalists Association condemned the violation of press freedom. Both arrests together constituted an "escalation of anti-media actions", it said.

The staff union of Next Media, the parent firm of , called his arrest unreasonable.

reporter Samuel Chan, who recorded Wong's arrest, said his attention was drawn to growing tension at a traffic junction as police tried to stop people crossing the road.

"That group of people gathered to wait to cross the road, and then the officers went in front of them," he said.

"I thought something might happen, so I raised my iPhone to capture the scene."

In other developments, Chief Superintendent Steve Hui Chun-tak told reporters the force was highly concerned about an officer suspected to be involved in the alleged unnecessary use of force on a "passer-by".

Hui declined to say if that officer, whom he did not name, would face a criminal investigation. He said the Complaints Against Police Office would handle the case "fairly and justly" and submit a report to the Independent Police Complaints Council.

In that case, a video by broadcaster DBC shows people apparently leaving the occupied zone peacefully on Thursday night. A superintendent uses his baton to hit two people walking by on their back and waist, while another pushes a man with a shield.

One of the civilians said yesterday that he was not a protester.

The man, who called himself Osman, told Commercial Radio: "I said at the time, 'Don't hit us. We are just passers-by. Here are members of the public and many girls'. Then I was hit twice."

Osman said his neck was injured. "I seriously doubt if they can control their emotions well."

Police sources indicated the officer shown in the clip was Sha Tin divisional commander Superintendent Chu King-wai.

"He has been removed from the 'Solar Peak' operation and has returned to his original post," a source said. "The alleged victim has not complained to police", but police had initiated follow-up action. Chu is a police veteran of over 30 years and is due to retire in four weeks when he turns 55.