WUHAN - An oilfield ship that capsized while under construction has been righted, the vessel builder Wuchang Shipbuilding Industry Company Ltd. said Saturday.

The company, a subsidiary of the China Shipbuilding Industry Corporation, confirmed that workers have drained water out of the ship and made it afloat again.

"No casualties or water pollution had been caused" and the cause of the accident was still being probed, the company said in a statement.

The statement said the ship, with a contracted value at 739 million yuan ($117 million), has been covered by full compensation insurance.

The ship is reported to have sunk during a test voyage in the harbor of Nantong City in Jiangsu Province.

"The ship tilted in shallow water near the dock after water poured in," the company spokesman Liu Zhengguo said, "but it did not sink."

He said that the cabin was flooded during maintenance between 1:30 pm and 2 pm on January 14, after a 400 mm x 600 mm manhole lid was accidentally removed.

"The ship capsized after about 15 minutes," the company said in the statement.

The Shanghai salvage bureau sent a 2,500-tonne crane to hoist the ship back up.

The multi-purpose anchor-handling tug supply vessel is owned by China Oilfield Services Ltd., a listed subsidiary of the China National Offshore Oil Corp. (CNOOC), the country's biggest offshore oil producer.

The CNOOC has been under public scrutiny after a string of oil leaks in 2011. Oil spills occurred in summer 2011 in the CNOOC Penglai 19-3 oil field, a joint venture with ConocoPhillips China, and in October in the Jinzhou 9-3 West oil field.

In December, a gas leak was found in a sub-sea gas pipeline of the CNOOC Zhuhai Hengqin gas processing terminal in the South China Sea before the company shut down a few platforms. No injuries or environmental pollution were reported.