In Tokyo, the greenback fetched 119.94 yen following the comments, from 118.51 yen in New York where it fell at one stage to 116.18 yen, its lowest level since February. The dollar was above 124 yen last week.
The euro bought 138.44 yen from 137.55 yen in US trading, while it slipped to USD 1.1541 against USD 1.1606.
A bloodbath on global equity markets driven by fears over a slowdown in China -- and the broader impact on the global economy -- pushed traders into the yen, which is seen as a safe haven in times of turmoil.
A rapid rise in the yen hurts major Japanese exporters such as Toyota and Sony by denting their competitiveness overseas and shrinking the value of repatriated profits.
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Economy Minister Akira Amari called for a "cool-headed approach", but added that the shift into the yen "reflected the strength of Japan's economic fundamentals".
"The foundations of the global economy have not been shaken -- a cool-headed approach is necessary," he told reporters.
Investor fears have spiked on concerns the world's second-biggest economy is slowing more than previously thought after China's central bank devalued the yuan in a shock move seen as a bid to boost sagging exports.
That has sparked fears over a currency war in which countries cut the value of the currencies to compete.
In other trading, Russia's currency fell again after the euro passed the symbolic 80-ruble mark yesterday.