China has been running down its vast foreign currency reserves in an attempt to boost the value of its own currency and stem a flow of funds overseas.
At $3.23 trillion, China still has the world's biggest reserve of foreign currency holdings.
But that has declined by $420bn over six months and stands at the lowest level since May 2012.
"While the remaining reserves still represent a substantial war chest, the mathematics around this rapid pace of depletion in recent months is simply unsustainable for any length of time," said Rajiv Biswas, Asia Pacific Chief Economist, IHS Global Insight.
Investor fear
The Chinese authorities fear a rapid devaluation of their currency, as it could destabilise the economy.
