Currency experts fear a potentially drastic fall in China's foreign reserves in October, a shock that risks reviving last year's currency panic and further rattling fragile world stock markets.

Capital Economics warns that the headline figure is likely to drop by $100bn, five times as much as in September and the highest level since the global equity rout in January and February. The official data is released tomorrow in Beijing.

This would inevitably ring alarm bells among skittish traders, already on edge over the US elections and over expected monetary tightening but the US Federal Reserve.

Three-month dollar LIBOR rates have jumped by a half to 0.89pc since June as liquidity is drained, raising the cost of borrowing for the world's dollarized financial system.

"There are notable cracks emerging under the surface," said Jens Nordvig from the specialist currency boutique Exante Data.

"The fairly orderly depreciation of the Chinese currency over the last few weeks has been achieved only in the face of an aggressive currency intervention by the Chinese central bank (PBOC). Eventually the cracks will reach the surface," he said.