Tokyo stocks jumped 1.59 percent to an eight-month high Thursday morning as a weaker yen buoyed Japanese exporters, with investors betting on more central bank easing.
The benchmark Nikkei 225 index rose 152.27 points by the break to 9,733.73, its highest point since early April, while the broader Topix index of all first-section shares rose 1.18 percent, or 9.33 points, at 800.62.
After a two-day meeting, the policy committee of the US central bank said it would replace its "Operation Twist" bond swapping programme with $45 billion a month in straight bond buys, on an open-ended basis.
That comes on top of the $40 billion a month purchasing announced earlier.
The Fed also provided a surprise by saying it would not lift rates as long as the inflation outlook was below 2.5 percent and the jobless rate, now at 7.7 percent, stays above 6.5 percent.
The Fed move has stoked expectations of further easing by the European Central Bank and Japanese policymakers, dealers said.
"The Fed's decisions did not really surprise anyone, although its comments about expecting rates to remain very low as long as unemployment remains above 6.5 percent were somewhat novel," said Hiroichi Nishi, general manager of equities at SMBC Nikko Securities.
"The bottom line is that it will continue its aggressive steps to foster economic growth," he told Dow Jones Newswires.
The yen sagged to multi-month lows against the euro and dollar ahead of Sunday's general election in Japan with the opposition Liberal Democratic Party, which wants the Bank of Japan to launch more aggressive easing measures, leading in polls.
Major Japanese exporters were higher as the yen slipped. A strong currency makes manufacturers less competitive overseas while shrinking their repatriated foreign income.
"The opposition Liberal Democratic Party looks poised for a big win Sunday, so if it can move on its BOJ/aggressive easing pledge, the dollar stands to gain a lot more -- perhaps to the 85 yen level short term," said Mitsushige Akino, chief fund manager at Ichiyoshi Investment Management.
"If that happens, automakers especially will be in for a great deal of bidding."
In Tokyo trade, Toyota rose 1.26 percent at 3,605 yen, Mazda Motor surged 5.14 percent to 143 yen, Sony gained 4.92 percent to 874 yen and Nikon jumped 5.40 percent to 2,378 yen.
On currency markets, the dollar was changing hands at 83.45 yen in midday Asian trade, its highest level since late March, up from 83.24 in New York Wednesday afternoon.
The euro was mixed at $1.3064 and 109.02 yen against $1.3075 and 108.85 yen in US trade.