SHANGHAI - Rescuers are still searching for 10 sailors missing after a cargo ship capsized and sank off Shanghai Tuesday night, the city's maritime search and rescue center said Wednesday.

Rescue divers found a four square-meter hole in the hull, believed to have directly caused the ship to sink.

"But the current is too fast for us to enter," said diver Luo Zaili.

A tonne of water would have quickly flood the ship through the hole, making it hard for the crew to escape, staff with the local Maritime Safety Administration told Xinhua.

The city's maritime search and rescue center has dispatched seven patrol vessels, three salvage ships and five other boats to join the search.

"The searching is still our primary task," said Huang Jianwei, head of local Maritime Safety Administration.

According to the local water traffic management center, the "Changping" loaded with 5,000 tonnes of steel, collided with another freighter before sinking in the anchorage near the Yangtze River estuary.

Thirteen sailors were on aboard. Only three have been rescued so far.