"The size of monetary easing announced yesterday far exceeded expectations," said analysts at DBS Bank Ltd. in Singapore in a commentary.
The Nikkei 225 in Tokyo closed 1.6 percent higher at 12,833.64, its highest finish since Sept. 1, 2008. Earlier in the day it surged more than 3 percent, breaking the 13,000 level.
Stock markets in Asia outside of Japan sagged, however.
Hong Kong's Hang Seng tumbled 2.7 percent to 21,726.90. Analysts said the fall reflected some nervousness about a recent outbreak of deadly bird flu in China. Six people have died and authorities have ordered the slaughter of all poultry at a Shanghai market where the virus was detected. The news hurt tourism and travel-related shares. Hong Kong-listed Air China plunged 9.8 percent and China Southern Airlines sank 8.5 percent.
South Korea's Kospi dropped 1.6 percent to 1,927.23, dragged down by political jitters over the latest tensions with Pyongyang. Australia's S&P/ASX 200 lost 0.5 percent to 4,891.40 as investors took profits after recent rallies
In Japan, the monetary easing measures pushed the yen sharply lower. On Friday, the dollar was up to 97.09 yen from 96.13 yen late Thursday.
Mark Williams, chief Asia economist at Capital Economics, said that the Bank of Japan's credibility rests on the success of the new direction the bank is taking.
"Markets are giving it the benefit of the doubt for now. But if the broad monetary aggregates and inflation don't show signs of a shift, the new-found trust in the capacities of the BoJ will rapidly fade," Williams said in a written commentary.
Benchmark oil for May delivery was down 67 cents to $92.59 per barrel in electronic trading on the New York Mercantile Exchange. The contract fell $1.19 on Thursday.
The euro rose against the dollar, to $1.3017 from $1.2939 late Thursday in New York.
AP Business Writer Pamela Sampson contributed from Bangkok