A pedestrian walks past an advertisement for Rolex watches in Shanghai, China, May 28, 2013. [Photo/IC]

Swiss watch exports have suffered their biggest quarterly drop since 2009 as the industry struggles with the strong franc and a slump in demand in the China.

The value of shipments fell 7.2 percent in the third quarter, the Swiss customs office has reported. Exports dropped 2 percent in the first nine months of the year to 15.8 billion francs ($16.5 billion), according to the Federation of the Swiss Watch Industry.

"The data casts a shadow over prospects for the year," the trade group said.

Waning demand in Hong Kong and the Chinese mainland has spread to other Asian markets such as Singapore, South Korea and Taiwan, weighing down an industry that accounts for a 10th of Switzerland's exports.

Last month, a Deloitte LLP report showed that Switzerland's watch executives are the most pessimistic in four years as an increasing minority sees a threat from smartwatches.

The mainland and Hong Kong last year accounted for a quarter of Swiss watch exports.

In the United States, the second-largest market, exports fell 18 percent in September, their steepest monthly drop in five years.

"The main reason for the drop is the Chinese," Patrik Schwendimann, an analyst at Zuercher Kantonal-bank in Zurich, said.

"Demand has declined locally because they don't buy as many watches as before. My biggest worry is how will this all work out going forward. Is it just temporary, or could it deteriorate?"