* Japan FX intervention pushes yen sharply lower, Nikkei up
* Weak U.S. manufacturing data weighs on stocks
* Treasuries up as traders expect BoJ to buy US debt
By Walter Brandimarte
NEW YORK, Sept 15 (Reuters) - The yen tumbled against the dollar on Wednesday after Japan began heavily selling its currency in foreign exchange markets, boosting Treasuries prices, while uncertainty about economic growth kept stocks flat.
China's yuan jumped against the dollar on Wednesday as U.S. pressure mounts again over the yuan's value.
Prices of short-dated U.S. Treasuries rose as traders anticipated the Bank of Japan may soon buy U.S. debt to park dollars coming in from its first intervention in more than six years. The intervention and weak U.S. manufacturing data weighed on world stocks.
Japan promised to keep intervening in the market to protect its fragile economic recovery. The yen had recently reached its highest level in 15 years, threatening Japanese exporters. [ID:nTOE68E02W]
Traders cited market estimates that Wednesday's efforts amounted to around 1.5 trillion yen ($17.67 billion).
"I think we're now going to see persistent official buying of dollar/yen in the near-term," said Adam Cole, head of currency strategy at RBC Capital Markets.
The yuan
The dollar jumped 3.09 percent to a 85.62 yen
Still, the dollar remains about 7.8 percent lower this year against the yen, which is seen by investors as a safe haven from concerns over global growth.
"Speculators have been long of yen so there is scope for further yen selling. But there's skepticism over whether the Japanese can change the trend as fundamentals haven't altered," said Beat Siegenthaler, a foreign exchange strategist at UBS.
Japan's intervention also helped send the euro, Australian dollar and sterling sharply higher on the day against the Japanese currency, although traders doubted Tokyo had bought anything other than dollars.
The euro was up 3.2 percent at 111.44 yen
Stories on yen strength, intervention: [ID:nECONJP]
PDF on yen's rise: http://r.reuters.com/zuz33p
Reuters Insider TV-Dlr bounce: http://link.reuters.com/fet63p
Graphic on yen strength: http://r.reuters.com/puw56n
Japan political risk: http://r.reuters.com/jyj83n
Japan's benchmark Nikkei stock index <.N225> rose 2.3 percent, supported by gains for exporters like Toyota Motor Corp <7203.T>, which climbed 3.8 percent.
But weak U.S. economic data weighed on world stocks, keeping the MSCI All-Country World index <.MIWD00000PUS> a touch lower by 0.1 percent.
U.S. industrial output decelerated in August while a measure of New York state business conditions slipped to its lowest level in more than a year, a sign that growth in the world's largest economy could be slowing.
"A lot of people are aware we're at the upper end of the range that we've been stuck in for a while, so you have a combination of having a nice recent run-up and a little bit of weak economic data," said Eric Kuby, chief investment officer at North Star Investment Management Corp in Chicago.
"What you're seeing is some traders saying we're going to take some profits here ... but what you're seeing is a pretty muted reaction."
The Dow Jones industrial average <.DJI> rose 32.20 points, or 0.31 percent, to 10,558.69, while The Standard & Poor's 500 Index <.SPX> was nearly stable at 1,121.06. The Nasdaq Composite Index <.IXIC> edged up 1.98 points, or 0.09 percent, to 2,291.75.
In Europe, the FTSEurofirst 300 <.FTEU3> of top shares slipped 0.22 percent, while the MSCI stock index for emerging markets <.MSCIEF> was 0.11 percent higher.
U.S. Treasuries' prices rose as Japan's intervention spurred bets that the world's No. 3 economy will reinvest their dollar purchases back into U.S. government debt.
The benchmark 10-year U.S. Treasury note
Oil prices fell 1.6 percent to trade below $76 a barrel, down for the second day, ahead of the U.S. government's weekly oil inventory report. (Additional reporting by Charlotte Cooper in Tokyo, Richard Leong and Leah Schnurr in New York)