A reported export surge in September is failing to dispel the gloom suffusing forecasts for China’s third quarter GDP growth, which several economists predict to slump to a five-year low.

One problem lies with the export numbers themselves, which raise suspicions that over-invoicing may once again be artificially inflating export statistics as Chinese smuggle hot money into the mainland from Hong Kong to take advantage of an appreciating renminbi.

“As in the past, over-invoicing is a key channel for hot money to enter China,” said Shen Jianguang, chief Asia economist at Mizuho Securities in Hong Kong. Shen noted that exports to Hong Kong rocketed by 34 per cent in September, the highest level seen since April 2013, when over-invoicing was considered to be rife.