WASHINGTON — Fear that the financial crisis is infecting once-healthy economies created another white-knuckle day for investors Friday, causing many currencies to plummet in value and stock indexes to tumble from Tokyo to New York.
The market gyrations laid bare that the currencies not only of developing countries, like Brazil, Ukraine and South Korea, but also developed countries like Britain are being devastated by the crisis. At one point, the pound sterling was down almost 5 percent against the dollar, its biggest drop since 1971.
Chilling new developments attested to the wide scope of the crisis, despite efforts by heads of state, central bankers and corporate leaders to stanch the bleeding. Cash flowed into the dollar and the Japanese yen, the two most sought-after safe havens in a storm-tossed world, as it fled from emerging markets.
Hedge funds and other investors are pulling money out of these countries on an immense scale, analysts said, and putting it into dollars and yen. There were few safe harbors, as commodities also tumbled. Government-backed mortgage bonds and debt issued by top-rated corporations were also dragged down in the undertow.
"This is a panic in the way of the fine 19th-century panics, where we all run around like headless chickens," said R. Jeremy Grantham, a well-regarded investor who had predicted stocks would tumble. "I have been in the business for 40 years, and I have never seen anything like this."
So great are the concerns among policymakers about the turmoil in currency markets that it has prompted talk of a coordinated intervention by the leading industrial countries in coming days, to quell the soaring dollar and put a floor under emerging-market currencies.
Such a move — in which the Federal Reserve and other central banks would sell dollars and yen, and buy other currencies — has been used extremely sparingly by the United States in recent years.
"The risk is huge, but it is appropriate at this point, because if the emerging markets go into default, the consequences would be catastrophic," said Kenneth Rogoff, an economist at Harvard.
When a developing country's currency loses value rapidly, it impedes the ability to pay back loans from Western banks. That could cause a rash of corporate or even government defaults — an aspect of previous financial crises in Asia and Latin America.
The downdraft of the pound and the euro — which fell to $1.26 against the dollar on Friday, its lowest level in two years — is less serious for the economic well-being of Britain and Europe than the deterioration of currencies like the Mexican peso or the Russian ruble.
Even if the Federal Reserve, the Bank of Japan and other central banks intervened in the foreign-exchange markets, it is not clear that it will reverse the pressure on these currencies.