Total losses from the subprime mortgage meltdown may be in the order of $50bn to $100bn, according to estimates cited by Ben Bernanke in testimony to Congress on Thursday.

The Fed chairman said:"There clearly will be some significant financial losses associated with defaults and delinquencies on these mortgages."

Mr Bernanke also cautioned Congress against legislating narrowly on China's exchange rate, rather than addressing this in combination with the need for structural reform.

He said the exchange rate was "not a subsidy in the legal sense" but rather the cause of distortions in the Chinese economy that channel resources towards exports rather than production for domestic demand.