Rumours swirled that Goldman Sachs and Barclays were among those liquidating positions amid unprecedented losses for funds that use sophisticated computer programmes to trade in the financial markets. These funds, called "quant" or "stat-arb" funds, use programmes designed using historical statistical data, and make millions of tiny trades, none of which are meant to affect the market and none of which involve big bets on the direction of particular assets. They are meant to be among the least risky of all the strategies used by traders.

A spokesman for Barclays Global Investors, one of the top five quant fund managers, said the turmoil appeared to have been triggered by deleveraging by some of the big stat-arb players. "At the moment we are maintaining our risk levels and we feel that our portfolios are positioned appropriately."

He declined to comment on whether Barclays has been liquidating positions or has suffered significant losses.

Some estimates suggest statarb funds could have lost 10% of their value since the start of August, but firm figures are impossible to calculate in real time and the scale of the damage may only become clear after the end of the month, when funds report performance figures.

Most of the funds are highly leveraged, borrowing money to beef up what would otherwise be meagre returns.

Two Goldman Sachs hedge funds have been among those liquidating positions.

The Global Alpha fund, its main in-house operation, has $9bn under management and its aggressive move to reduce its positions prompted rumours that it was shutting down entirely. The stories are "categorically untrue", the company said.