Over-invoicing of Chinese imports ramped up in December as capital flight intensified amid market turmoil and continued depreciation of the renminbi.

Inflating the value of imports from Hong Kong to China is commonly used to move cash out of the country and the method has come back into favour as authorities in China clamp down on official channels of taking cash abroad.

Imports from Hong Kong to China jumped 64 per cent year on year in December, according to China customs data. The same numbers released by Hong Kong customs officials showed only a 0.9 per cent increase, indicating the mainland figures were greatly overvalued. A discrepancy between the two sets of data is normal and Chinese authorities have over the years tolerated it. But the extent of the divergence in December suggests much greater use of one of the few conduits for bringing money out of China.