The dollar hit a four-year high against the yen on Tuesday, stalling just shy of the 100 mark and tipped to rise further, though it could face some resistance given the rapid pace of its ascent.
Analysts said option barriers at 100 yen and traders taking profits has slowed the yen's fall, but it was only a matter of time before it broke lower again following the aggressive easing measures announced last week by the Bank of Japan.
The dollar was last down 0.4 percent on the day at 98.98 yen, having earlier risen as far as 99.67 yen, its highest since May 2009.
"There is a likelihood we could hit 100 yen relatively soon after the BoJ's massive stimulus move," said Saeed Amen, FX strategist at Nomura. "The risks are to the upside for dollar/yen but there are options barriers around the 100 yen level which need to go out so it could take some time... perhaps within the next week."
Traders also cited strong demand to take profit on dollar gains ahead of around 99.73 yen, the 50 percent retracement of the dollar's fall from the June 2007 peak of 124.14 yen to a record low of 75.311 set in October 2011.
Since BoJ Governor Haruhiko Kuroda promised on Thursday to inject about $1.4 trillion into the economy in less than two years, the dollar has gained more than 7 percent against the yen while Japanese stocks have jumped.
The euro hit 129.935 yen on the EBS trading platform, its highest since January 2010, before stalling just shy of 130. It last traded down 0.2 percent at 129.06 yen.
Traders said large stop-loss buy orders would be triggered if the euro broke through 130 yen. Japanese Finance Minister Taro Aso said on Tuesday that the yen was undergoing a correction from previous "excessive" rises, though he stressed the country's monetary policy was aimed at beating deflation not weakening the yen.
Dollar/yen one-month risk reversals, a measure of the relative demand for bets on the dollar rising against the yen over bets on it falling, have risen to around 0.7 in favour of yen puts since the BOJ announcement.
With the dollar stalling ahead of the 100 yen mark, however, risk reversals have dropped back to around 0.5 in favour of yen puts. But analysts said this pause was temporary. "Dollar/yen has moved so quickly it is bound to have setbacks ahead of key levels, so I am not surprised it is not just flying through the 100 mark," said Niels Christensen, currency strategist at Nordea in Copenhagen.
"(But).. everything is pointing to a weaker yen and everyone is happy to go with the flow."
The euro was up 0.3 percent at $1.3043, having hit a three-week high of $1.3068 earlier after stop-loss buying was triggered near $1.3050. The Australian dollar hit its highest since July 2008 at 103.81 yen and the New Zealand dollar rose to its highest since February 2008 at 84.49 yen.