Wall Street gave up some earlier gains as concern about weak US economic data outweighed the reassurance that global central banks remain more committed than ever to bolster growth.
Bank of Japan Governor Haruhiko Kuroda began his term with a larger-than-expected boost to kick-start the Asian nation's economy including plans to purchase 7 trillion yen (US$73 billion) of bonds a month.
"This is an unprecedented degree of monetary easing," Kuroda told reporters, according to Reuters. "We took all available steps we can think of. I'm confident that all necessary measures to achieve 2 per cent inflation in two years were taken today."
The yen sank more than 3 per cent against the greenback, posting a similar loss against the euro.
"They eased a lot more than anticipated," Vassili Serebriakov, a foreign-exchange strategist at BNP Paribas in New York, told Bloomberg News. "It's a much more aggressive move than the investors expected. Markets weren't necessarily positioned for this."