More Chinese rescue ships and helicopters have been mobilized to search for the 17 missing seamen after a cargo ship sank off northeast China, but little progress has been achieved so far, local maritime sources said.

Three rescue vessels, two helicopters and a fixed-wing aircraft, all of them from the Beihai Rescue Bureau under the Ministry of Communications, are searching a wider area, said the Dalian Maritime Rescue Center.

The "Ryong Ak San", belonging to the Democratic People's Republic of Korea's fishery authorities, sank near Laotiekou, Lushunkou District of Dalian, Liaoning Province on Tuesday afternoon.

It was on its way to the Jingtang Port in north China's Tianjin from the DPRK's western port city of Haeju with 2,900 tons of ore and 25 crew members aboard when it sank, the center said. The vessel's loading capacity is 3,000 tons, the center said.

Eight seamen were rescued Tuesday, but 17 others were missing.

"All the eight rescued seamen are in good shape," said Guo Zirui, vice director of the Liaoning Provincial Maritime Bureau. The eight now stay in a hotel of Dalian.

Five other merchant ships passing by the site were also asked to join the search, according to the bureau.

Vessels from a Chinese navy base in Dalian also joined the search.

"The search and rescue work is extremely difficult in the high winds, but we will do our best," said Guo.

He said the missing men probably had little chance of survival beyond Wednesday in the freezing waters and high seas.

The Dalian maritime rescue center received a report from another vessel, the "Guangyuan", at 3:08 p.m. Tuesday, saying a ship had suddenly sunk one nautical mile ahead of it.

"An emergency operation was immediately launched to search for the crew of the ship," said He Jianzhong, director of the center.

A helicopter from the Beihai No. 1 Air Rescue Squad in Dalian and rescue vessels from the Beihai Rescue Bureau were at the site immediately after the report, said He, also vice mayor of Dalian.

Minister of Communications Li Shenglin has instructed rescue workers to make every effort to search for the missing seamen. Contact with the DPRK via diplomatic channels is also underway.