Tokyo shares rose 1.29 percent to a near five-year high on Wednesday morning, supported by a solid performance on Wall Street and optimism over Japanese exporters' earnings thanks to the weaker yen.
The benchmark Nikkei 225 index was up 173.97 points at 13,703.62 by the break, topping 13,700 for the first time since June 2008.
The Topix index of all first-section issues gained 0.79 percent, or 9.02 points, to 1,152.80.
"Stock market gains have become more incremental as the Nikkei has continued to rise through 13,000," said Mitsushige Akino, chief fund manager at Ichiyoshi Investment Management.
On the other hand, "the dollar faces increased resistance as it nears 100 yen," he added.
The dollar's rise against the yen, triggered by massive monetary easing by the Bank of Japan, has stalled before hitting 100.00 yen, a level the greenback last broke in April 2009.
The dollar bought 99.29 yen in Tokyo midday trade, down from 99.48 yen in New York but still up from 98.81 yen in Tokyo Tuesday afternoon.
The euro fetched $1.2990 and 129.07 yen compared with $1.2997 and 129.30 yen in New York.
Mitsubishi Motors jumped 6.66 percent to 112 yen after the automaker nearly tripled its net profit estimate to 38 billion yen for the year ended in March, helped by lower costs and foreign exchange gains owing to the weaker yen.
Other major carmakers were also higher, with Nissan Motor up 2.12 percent at 1,056 yen and Toyota Motor rising 0.90 percent at 5,560 yen.
A lower yen benefits Japanese exporters as it makes their products more competitive abroad and increases their income when repatriated.
In New York on Tuesday the Dow Jones Industrial Average finished up 1.05 percent at 14,719.46, helped by good earnings results from DuPont, Travelers and other firms.
The market spent most of the day in positive territory, save for a brief plunge after a bogus tweet from a hacked Associated Press account said there had been two explosions at the White House and President Barack Obama had been injured.
The AP almost immediately announced it had been hacked and the message was false.