The business for offshore oil is very much the operators' main profit source, contributing about 80 percent to COHC's total income in the past two years, adds Liu, taking it to 987 million yuan ($155.15 million) in 2011, a 12.2 percent increase from 2010.

"The business for offshore oilfields supplies the cash flow to our company," says Jian Zhuodong, of China Southern Airlines.

Oil exploration firms generally pay the helicopter operators a daily rental fee for their services, and extras can be charged depending on flight times. But as in any growing market situation, the more business there is, the more competition arrives.

"We do worry about a price war in the field, and the competition is getting harder," says Jian, explaining that offshore business is almost many operators' only profitable arm, despite still undercutting international prices by around 10 percent.

In COHC's recent annual report, the firm called maintaining its leading position in the offshore marketplace "more challenging than ever", meaning all the Chinese helicopter operators are being forced to invest in their fleets.

"We have heavy pressure now," adds Liu, the deputy general manager. Its fleet and service upgrading will continue apace, he says.

The leading operator bought seven EC225 helicopters from Eurocopter in December 2011, the manufacture's largest type, having 19 seats. COHC plans to supply multiple services using its various helicopters, including training, maintenance and onshore service.

Eurocopter got orders worth 300 million euros ($381 million) in China in 2011, more than double its 2010 sales.

Future activities such as oil prospecting, oil pipe patrols and other work also present massive further potential business for operators, as well as offshore wind power projects.

"I believe wind farm could be an important customer for helicopter operators in the future," adds Bernd Brucherseifer, managing director of HTM Helicopter Travel Munich GmbH in Germany, one of the world's oldest helicopter operators working on offshore wind farms.

Christopher Grainger from Eurocopter says his order book is open and ready for the Chinese offshore helicopter industry to continue to boom.

"Business will be larger in the future," he says.

wangwen@chinadaily.com.cn