* Dollar, euro on pace for best day vs yen since 2008 * BOJ pledges to pump $1.4 trillion into economy * ECB's Draghi says "ready to act," Cyprus no template By Gertrude Chavez-Dreyfuss and Wanfeng Zhou NEW YORK, April 4 (Reuters) - The dollar and euro soared more than 3 percent against the yen in their biggest one-day moves since 2008 on Thursday after the Bank of Japan announced a level of monetary easing to fight deflation that was seen as a radical overhaul of policy. The BOJ pledged to inject about $1.4 trillion into the economy in less than two years. Governor Haruhiko Kuroda, chairing his first policy meeting, committed the BOJ to open-ended asset buying and said the monetary base would nearly double to 270 trillion yen ($2.9 trillion) by the end of 2014. "The BOJ has set in play a very aggressive expansion of monetary policy, and it's very likely dollar/yen will continue to rise," said Lee Hardman, currency economist at BTMU, adding the dollar could hit 100 yen in the next three to six months. The dollar rose as high as 96.39 yen, near a 3-1/2-year peak of 96.71 set on March 12. It was last trading at 96.37 yen, up 3.6 percent on the day and on track for its best day since October 2008. The euro soared 3.6 percent to 123.87 yen, the biggest one-day move since November 2008. Traders said the yen's falls were magnified because before the announcement the market had prepared for the BOJ to deliver less than expected, as it had done in the past. The BoJ shocked markets in what was seen as a radical overhaul of policymaking, shifting the policy target to the monetary base from the overnight call rate and ditching its previous stance of shunning long-term bonds. The yen extended losses as Kuroda said he would not hesitate to adjust policy further. Market players said Japanese institutional investors were also likely to increase overseas investments, which could trigger "the next leg" in yen weakness. The BOJ's new plan means it will buy about 7 trillion yen ($73 billion) of bonds per month, equivalent to about 1.4 percent of gross domestic product. By comparison, the U.S. Federal Reserve is buying $85 billion of bonds per month - about 0.6 percent the size of the economy. The yen also weakened against other currencies, with the Australian dollar rising above 100 yen for the first time since 2008. The euro was little changed versus the dollar in choppy trade after European Central Bank President Mario Draghi said the bank stood "ready to act" if growth continues to languish, and he affirmed his commitment to keeping the euro zone intact. He also said the Cyprus bailout was not a "template" for future rescues in the currency zone. The euro was last flat at $1.2852. It had earlier dropped to $1.2745, its lowest in more than four months as Draghi highlighted the downside risks to the euro zone economy, suggesting the bank could further slash interest rates.