Fears of a deepening of Europe's debt crisis have prompted the world's leading central banks to pump US dollars into the financial system, in a co-ordinated action designed to boost market confidence.

The Bank of England joined the US Federal Reserve, the European Central Bank, the Swiss National Bank and the Bank of Japan on Thursday to announce that they would flood money markets with dollars over the coming months.

The move, on the third anniversary of the collapse of the US investment bank Lehman Brothers, sent shares soaring in banks heavily exposed to debt default by Greece and the other struggling members of the 17-nation eurozone. The euro, which had been falling in recent days, rebounded, rising roughly 1% in European trading on Thursday.

Speaking in Washington, Christine Lagarde, the president of the International Monetary Fund, said: "They [the banks] are getting together and acting together. To me, that is the most important message."

Lagarde warned that more action was needed.

"We have entered into a dangerous phase of the crisis," she said. There is still a path to recovery, Lagarde said, but it is a "narrow" one....