A deepwater oil exploration vessel belonging to China Oilfield Services Ltd. (HKG:2883) sank Saturday during construction at a dock in east China, the company said in a statement to the Shanghai Stock Exchange Wednesday.

The company is the listed rig builder and drilling-equipment arm of China National Offshore Oil Corp. (CEO), China's largest offshore oil producer.

Water entered the supply vessel's hold while it was under construction at a dock in Nantong city in Jiangsu province around 2 p.m. Saturday. China Oilfield said no environmental pollution resulted, adding that it is investigating the accident.

The company also said Wuchang Shipbuilding Industry Co., the shipbuilder, should be held accountable for losses.

China Oilfield had invested CNY740 million ($117 million) in the vessel's construction.

Cnooc last month said it may begin independently drilling its first deep-sea gas exploration well in the South China Sea by early 2012. It isn't immediately clear if Saturday's accident would affect those plans.
Cnooc has been under pressure after a string of oil leaks in 2011. In December, a gas leak at one of its pipelines in the South China Sea forced it to close some platforms.

The company's Penglai 19-3 oil field, a joint venture with ConocoPhillips China, and the Jinzhou 9-3 West oil field were also sites of oil spills last year.