Fallout from North Korea's first nuclear test wiped out the dollar's eight-month high against the yen as the markets reacted to the news.

In other trading, sterling hit a one-week low against the dollar, falling around 0.3 per cent over the day, although it remains eight per cent up on January, and fell 0.3 per cent against the euro.

"The impact on dollar-yen won't last long," Joseph Kraft of Morgan Stanley in Tokyo told Bloomberg.

"The markets, especially overseas markets, have been very calm after the test.

"The nuclear test does not necessarily mean North Korea immediately launches an atomic bombing on Japan," he added.

Gains in the dollar earlier in the day followed market speculation that Japanese investors would shift their attention to perceived safer investments, including the US treasuries.

An announcement by Japan's economic minister Hiroko Ota that the real effective exchange rate was likely to weaken further also caused the yen to fall.

Nuclear test shakes markets