Eleven crew of a Chinese cargo ship are missing following a collision with a large container ship in the waters off Hong Kong on Monday, authorities said.
Hong Kong is one of the world's busiest shipping channels, although serious accidents are rare.
The cargo ship Zhong Xing 2 sank after the collision with the 300-m- (984-ft-) long Marshall Islands-registered MOL Motivator about two nautical miles southwest of Po Toi Island, a spokeswoman of the Hong Kong Maritime Department said.
"Zhong Xing 2 is suspected to have sunk after the collision, and it is reported there are 12 crew onboard," said the spokeswoman, who declined to be identified in line with department policy.
"One of them was picked up by a fishing vessel navigating close by," she added. The remaining 11 crew of the Chinese ship were reported missing.
Rescue efforts were being co-ordinated by the Guangdong Rescue Co-ordination Centre as the incident happened outside Hong Kong waters, the spokeswoman said.
Hong Kong's Marine Rescue Co-ordination Centre is assisting the rescue and has deployed one helicopter, five marine police launches and three fire service department launches.
MOL Motivator, which has a dry weight tonnage of 79,400 tonnes according to Thomson Reuters data, was travelling from Hong Kong to Yantian port in southern China.
Hong Kong is the world's fourth largest container port, after neighbouring Shenzhen, which occupies third place.
Vessels navigating near the collision site have been warned there may be a sunken ship nearby and have been asked to stay away.
The Hong Kong Observatory issued an amber rain warning, signalling expectations of heavy rain in parts of the territory overnight.
Thirty-nine people died in the city's worst maritime disaster in more than 40 years in October 2012 when a high-speed ferry and a pleasure boat collided.
Reporting by Alice Woodhouse