A man was found unconscious about 20 metres offshore from Wong Shek Pier in Sai Kung after police received a report of a suspected drowning at about 10pm on September 26.
Rescue personnel, including fire-service divers, located him floating in the water. Firefighters brought him back to shore.
He was then taken by ambulance to Tseung Kwan O Hospital for emergency treatment.
Police are investigating the cause of the incident, which has been provisionally classified as a person drowning.