A workship worth an investment of 740 million yuan (117 million U.S. dollars) by a leading Chinese oil field service provider has sunk during construction at a dock in east China.

The cause of the accident is being investigated and no environmental pollution was incurred, the China Oilfield Services Ltd. (COSL) said in a statement to the Shanghai Stock Exchange on Wednesday.

The high-powered deep-water anchor-handling tug supply vessel bilged while under construction at a dock in Nantong city, Jiangsu province, on Jan. 14, according to the statement.

Wuchang Shipbuilding Industry Company Ltd., the builder of the ship, should take responsibility for losses caused by the accident according to contracts, it said.

The COSL is 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. A gas leak was found in a sub-sea gas pipeline of the 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.

Oil spills occurred in the 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.

COSL shares fell 1.8 percent in Shanghai as of 2:30 p.m. on Wednesday.