BANGKOK (AP) - Japan's benchmark stock index surged above 13,000 for the first time in more than four years Friday, its second straight day of big gains after the central bank announced aggressive action to lift the economy out of a prolonged slump. The Bank of Japan unveiled plans Thursday to pump huge amounts of money into the financial system in order to spur price rises, spending and borrowing in an economy that has stagnated for years. The central bank said it wanted to double the money supply and achieve a 2 percent inflation target within about two years. The sweeping shift in monetary policy came as a surprise to analysts, even though the BOJ's new governor Haruhiko Kuroda has vowed to do whatever necessary to break Japan's economy out of its deflationary malaise. Falling prices have stunted growth in the world's No. "The size of monetary easing announced yesterday far exceeded expectations," said analysts at DBS Bank Ltd. in Singapore in a commentary. The BOJ's plans include buying $530 billion a year in government bonds. Kuroda described the scale of monetary stimulus as "large beyond reason," but said the inflation target would remain out of reach if the central bank stuck to incremental steps. Mark Williams, chief Asia economist at Capital Economics, said that the BOJ'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. The Nikkei 225 in Tokyo was up 3 percent at 13,010.73. The benchmark has soared 25 percent this year, rejuvenated by Prime Minister Shinzo Abe's election in December and enthusiasm for his economic and monetary program that favors a massive expansion of the money supply to create inflation and jolt Japan out of its slump. A cheaper currency makes Japanese goods less costly overseas and raises the value of repatriated profits. Nissan Motor Co. jumped 6 percent. Ricoh Co. advanced 6.1 percent. Heavy-equipment maker Komatsu soared 7.6 percent. Japanese banks also benefited. Mitsubishi UFJ Financial Group gained 5.9 percent. The dollar rose to 96.30 yen from 96.13 yen late Thursday. The dollar was at about 92.80 before the BOJ's two-day policy meeting ended with its dramatic announcements Thursday and before Abe's Dec. 16 election was trading around 80 yen. Hong Kong's Hang Seng tumbled 2.4 percent to 21,807.27. 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 11.3 percent and China Southern Airlines sank 11.6 percent. South Korea's Kospi dropped 1.7 percent to 1,926.05, dragged down by political jitters over the latest tensions with Pyongyang. Australia's S&P/ASX 200 lost 0.4 percent to 4,896.20 as investors took profits after recent rallies. Benchmark oil for May delivery was down 4 cents to $93.22 per barrel in electronic trading on the New York Mercantile Exchange. The euro fell to $1.2926 from $1.2939 late Thursday in New York.