China's exports in the third quarter may be hit by falling demand, the General Administration of Customs said on Wednesday.

The China Export Leading Index registered 36.1 percent at the end of June, down from 37.6 in May, Zheng Yuesheng, customs, spokesman for the administration, told a news conference on Wednesday.

The index, launched in June 2012, tries to forecast foreign trade trends over a three-month period.

The latest survey showed that 49.2 percent of enterprises reported smaller orders from a year earlier while 43.8 percent were "not optimistic" about the outlook over the three months.

Hu Yuexiao, an economist at Shanghai Securities, said that exports could see a period of stagnation.