Port workers in East China's Jiangsu province are still working to salvage an offshore oilfield vessel that capsized during construction on Jan 14.

The ship, worth 740 million yuan ($117 million), was reported to have sunk during a test voyage in the harbor of Nantong city in Jiangsu.

But a spokesman with China Shipbuilding Industry Corporation (CSIC) said such reports were untrue.

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

Liu did not say how the accident happened.

The shipbuilder, Wuchang Shipbuilding Industry Company Ltd under the CSIC, said the cabin was flooded during maintenance between 1:30 pm and 2 pm on Jan 14, after a 400 mm x 600 mm manhole lid was accidentally removed.

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

The Shanghai salvage bureau has sent a 2,500-ton crane to hoist the ship back up. The operation continued Wednesday afternoon, it said.

The company said no casualties or water pollution had been caused and the accident was still being probed.

The accident caused a 1.8 percent fall in CSIC shares in Shanghai Wednesday afternoon.

The multi-purpose anchor-handling tug supply vessel is owned by China Oilfield Services Ltd (COSL) and would undergo repairs at the dock after the emergency salvage operation.

COSL is a listed subsidiary of the China National Offshore Oil Corp (CNOOC), the country's biggest offshore oil producer.

CNOOC has been under public scrutiny after a string of oil leaks in 2011. And a gas leak was found in a sub-sea gas pipeline of CNOOC's Zhuhai Hengqin gas processing terminal in the South China Sea in December, forcing the company to shut down some platforms. No injuries or environmental pollution were reported though.

Oil spills occurred in CNOOC's Penglai 19-3 oil field, a joint venture with ConocoPhillips China, in the summer and the Jinzhou 9-3 West oil field in October.