The euro cannot replace the dollar as the world's main reserve currency, and a system of two reserve currencies would be unstable, billionaire investor George Soros said on Thursday.

"I don't think the euro can replace the dollar, and a system with two major reserve currencies is not a stable system," Soros said.

The euro has surged to record highs against the U.S. currency as the U.S. economy is seen going into recession.

"What we have now is a period of instability and heightened uncertainty," Soros said.

He was in Brussels to promote his latest book, "The New Paradigm for Financial Markets: The Credit Crisis of 2008 and What It Means".

It was still a time of wealth destruction, Soros said, and he advised investors to find ways to preserve capital until it was clear how the authorities and markets would respond.

He said the main lesson from the current financial market turmoil was the need to control credit and not just money supply, and added that markets were not yet out of trouble.

"There is a commodities bubble still in the growth phase while other bubbles are being deflated," Soros said.

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