FRANKFURT — An organization representing the world’s main central banks warned on Sunday that dangerous new asset bubbles were forming even before the global economy has finished recovering from the last round of financial excess.

Investors, desperate to earn returns when official interest rates are at or near record lows, have been driving up the prices of stocks and other assets with little regard for risk, the Bank for International Settlements in Basel, Switzerland, said in its annual report published on Sunday.

Recovery from the financial crisis that began in 2007 could take several more years, Jaime Caruana, the general manager of the B.I.S., said at the organization’s annual meeting in Basel on Sunday. The recovery could be especially slow in Europe, he said, because debt levels remain high.

“During the boom, resources were misallocated on a huge scale,” Mr. Caruana said, according to a text of his speech, “and it will take time to move them to new and more productive uses.”