Ten crew are missing and three were rescued after a cargo ship sank near Shanghai's Wusong Dock on Tuesday night.
The sunken ship Changping was loaded with 5,000 tons of steel.
The maritime search and rescue center said it first received a report of the collision at 11:39pm on Tuesday.
According to Wusong water traffic management center's tracing record, Changping collided with a freighter at 11:30pm before sinking in the anchorage near Yangtze estuary.
Three crew — including the chief mate — had been rescued by 1am, Shanghai Maritime Bureau said. Two of them were saved by a boat passing by. The third was saved by Xinwang 138, the ship that Changping was in collision with. All three were in stable condition.
Nearly 20 search and rescue boats were sent to the scene to continue searching for the missing sailors. A helicopter joined the search at 6:30am yesterday.
The search and rescue center's tracing record showed that Changping left its basin at 11:06pm, and started to speed up at 11:25pm. Five minutes later, it collided into Xinwang 138, which was berthing at its basin.
The center then lost trace of Changping, but received a collision report from Xinwang 138, saying Changping was sinking.
A rescue diver's report said there was a 4-square-meter hole at the stern of the sunken ship, which very likely led to its sinking. "But the current is too fast for us to enter," Xinhua news agency quoted diver Luo Zaili as saying.
A ton of water would have quickly flooded the ship through the hole, making it hard for the crew to escape, staff with the local Maritime Safety Administration told Xinhua.
The water depth is about 12 meters in the area. The maritime bureau said the cause of the incident was still under investigation.
Search for the missing crew will continue for at least three days before the authority starts salvaging the sunken ship and freight, bureau officials said.
"The searching is still our primary task," said Huang Jianwei, head of local Maritime Safety Administration.