The footage showed two policemen repeatedly hitting Chung in the head, abdomen and genitals.

Chung had been arrested on suspicion of assaulting police the previous day in an incident not related to the ongoing protests sweeping the city. Three policemen were arrested in connection with the incident on Tuesday. One of them, a plain-clothes officer, has resigned.

On Wednesday police said in a press conference that the officer in charge of looking into complaints by Chung’s family had assumed there were no security cameras at the scene and did not clarify with the hospital.

Police earlier also claimed to be unaware of the presence of security cameras inside the room where Chung, who was drunk at the time of his arrest, was taken.

“Based on our understanding, there are usually no surveillance cameras in wards, so we will approach the hospital later on this,” John Tse Chun-chung, chief superintendent of the force’s public relations branch had said.

On Tuesday, Tse said it was the footage made public by Democratic Party lawmaker Lam Cheuk-ting that triggered a criminal investigation and the arrest of three officers the same day.

But signs telling people they are under round-the-clock video surveillance could be seen on the doors of two disturbed patient rooms at the hospital in question on Tuesday night.

“This area is under 24-hour closed circuit television monitoring and recording for the purpose of ensuring your security and safety when visiting our premises,” the signs read.

They were spotted alongside labels that read, “Disturbed Patient Room”.

A hospital spokeswoman confirmed on Wednesday that the signs warning of video surveillance “have always been posted” near the rooms.

The two rooms, 7 and 7A, are metres away from a nursing station in an open area inside the emergency department, connected by a corridor.

According to Lam, who was given the footage and made it public on Tuesday, Chung was held in room 7A.

Multiple frontline medical sources confirmed security cameras are installed inside such rooms in public hospitals and the lenses are usually not hidden.

“The security cameras inside disturbed patient rooms are easy to spot,” a source said, adding security footage is shown on monitors at nursing stations.

A hospital spokesman said on Tuesday that Chung was guarded by police throughout his stay and medical staff saw “no abnormal situation”.

The hospital has not yet explained why staff did not intervene or enter the room during the incident, which spanned more than 20 minutes.

The Post has asked the Hospital Authority, which manages all public hospitals in Hong Kong, for access to view the rooms in question.

At the Wednesday press conference, Tse admitted that the officer in charge of looking into the complaint had made a “wrong judgment” in assuming there were no security cameras on site.

He added that this decision was based on past experience as there were seldom security cameras inside hospital wards. Tse also said the officer’s methods could be improved, but refused to confirm if police would apologise to Chung and his family or the wider public over the incident.

He added that police guidelines stipulated all officers should prioritise criminal investigations, such as the allegations of assault against Chung, over complaints.

According to Chung’s family, the man was arrested on June 25 and only brought up the alleged assault by policemen after he was released the following day.

Chung’s sons then filed a complaint with police on June 27, but were said to have not responded to requests to provide more information.

They filed another complaint against police on Wednesday.

Lam said police had not taken the complaint from Chung’s sons seriously.

“The signs are clear, but I don’t know if the officers involved had noticed,” Lam said.

Lam also said police could have easily learned about the existence of the cameras.

“If we did not get the footage, police would have done nothing,” Lam said. “Whether there were security cameras or not, they should not have beaten someone up.”