WASHINGTON — The Federal Reserve and other major central banks moved on Wednesday to help foreign banks more easily borrow and lend money, seeking to forestall a breakdown of global financial markets and giving Europe more time to wrestle with its debts. The latest round of interventions by central banks, including the expansion of an existing Fed program that lets foreign banks borrow dollars at a low interest rate, reflects growing concerns that Europe’s financial problems are hampering growth.

In a sign that the fallout is increasingly global, the Chinese central bank, which has sought to slow an overheated economy and inflation over the last year, also moved unexpectedly but independently Wednesday to encourage new lending by Chinese commercial banks.

In Europe and the United States, where the announcement broke well ahead of stock market openings, the prospect of more cheap money to ease banks’ operations sent stock indexes soaring. A broad index of German stocks, the DAX, jumped almost 5 percent Wednesday, while the broad measure of American stocks, the Standard & Poor’s 500-stock index, climbed more than 4 percent. Short-term borrowing costs also declined modestly for some European governments and banks.

But policy makers and analysts were quick to caution that the Fed’s action did not address the fundamental financial problems threatening the survival of the European currency union. At best, they said, efforts by central banks to ease financial conditions could allow the 17 European Union countries that use the euro sufficient time to agree on a plan for its preservation.