"We're seeing a major reversal of the dollar's fortunes," said John Doyle, vice president of dealing and trading at Tempus, Inc.
With US rates much higher, and the scope for them to fall much wider, investors are reversing out of the dollar.
"Rate cut expectations have gained momentum and US rate expectations are falling a lot more than they are in the euro zone," said Thu Lan Nguyen, an analyst at Commerzbank.
Whether or not the dollar retreats further depends on economic data on the coronavirus's impact on confidence and trade outside of China, Nguyen said.
Against the euro, the dollar fell to a three-week low, last down 1.14% to 1.100. The dollar index dropped 0.76% to 98.358, its weakest since Feb. 6.
It has shed roughly 1% since last week, when it touched a near 3-year high thanks to its safe-haven currency credentials and investors' belief that the US economy was relatively sheltered from the coronavirus fallout. But the currency's safe-haven appeal has worn off.
One-month volatility in euro/dollar, which was near record lows, has shot up to its highest since early October.
The dollar dropped 0.58% to 109.77 Japanese yen as the yen's safe-haven appeal began to return.
China's offshore yuan strengthened to a one-week high, with the dollar down 0.2% at 7.007 yuan per dollar. The Australian dollar, seen as a proxy for investor sentiment towards China, rebounded 0.67% to $0.659, away from 11-year lows touched on Wednesday.