The Zhong Xing 2, which was laden with cement, went down after colliding with a container ship in the early hours yesterday just south of the island of Po Toi, on the edge of Hong Kong's maritime territory.
A 46-year-old mainland Chinese crewman is so far the sole survivor of the ship's crew of 12 -- he was plucked from the sea by a passing fishing boat.
Chinese authorities are coordinating the rescue operation, sending 15 ships and three helicopters to hunt for the missing crew, according to China's official state news agency Xinhua.
"We are still trying to find the wreckage and the missing 11 persons," a Hong Kong government spokesman told AFP.
The cause of the accident is not yet known and is under investigation, he said.
The 97-metre Zhong Xing 2, which was carrying cement from the Chinese province of Hebei to the southern island of Hainan, collided with the Marshall Islands-registered MOL Motivator container ship -- more than three times its size.
The cargo ship sank two nautical miles (around four kilometres) south-west of Po Toi.
The collision between a high-speed ferry and a pleasure boat shocked the Asian financial hub, which prides itself on its good safety record.
Waters around the territory are notoriously crowded with hundreds of vessels -- from tiny wooden fishing boats to gigantic container ships -- plying the routes to and from one of the world's busiest ports.
In other major incidents, a 190-metre long cargo ship sank 80 kilometres south-west of Hong Kong in August 2013, when a powerful typhoon generated towering waves.
