Nearly three-quarters of American firms in Shanghai say China's first free trade zone (FTZ) offers them no business benefits almost 18 months after it was established, according to a survey Wednesday.

The Chinese commercial hub set up the FTZ in September 2013, promising a range of financial reforms, including full convertibility of the yuan currency and free interest rates, which remain unfulfilled.

"More than one year after the FTZ's opening, US companies remain sceptical about the business benefits," the American Chamber of Commerce in Shanghai said in its annual business climate report, released on Wednesday.

A total of 73 percent of the 377 member companies answering the survey said the FTZ offers "no tangible benefits" for their business, and almost half of them reported no noticeable changes for their operations so far.

But the US business group said the FTZ had brought improvement in customs procedures in Shanghai.

Around a quarter of companies surveyed said they had already established a presence in the FTZ or planned to do so, despite the slow start, it said.

China's national government has already announced intentions to expand some reforms from the first FTZ nation wide, while three more locations plan to set up their own zones.

In January, Shanghai Mayor Yang Xiong pledged greater efforts towards financial liberalisation in the FTZ but made clear they would depend on central authorities.

The business climate survey also showed that more than half of respondents believed China's regulatory investigations are more likely to "target" foreign companies, following a series of high-profile probes.

Last month, US mobile chip titan Qualcomm agreed to pay nearly $1.0 billion to end a long-running antitrust probe in China, the biggest such fine ever levied by Beijing.

Over the past two years, Chinese authorities have stepped up scrutiny of foreign firms, launching sweeping investigations into alleged malpractice in sectors ranging from pharmaceuticals to baby formula.