* Turkey's move raises hopes of turnaround in emerging market rout
* Buying driven by short-term players, investors look to Fed
* Advantest hits near 4-month low on outlook cut
TOKYO, Jan 29 (Reuters) - Japan's Nikkei average jumped almost 2 percent on Wednesday morning after four days of losses as Turkey's huge hike in interest rates halted selling in emerging markets and bolstered risk appetite. But shares of Advantest plunged to a near four-month low after the company slashed its full-year guidance, underscoring the risk of more disappointment as many Japanese companies report earnings over the next few weeks. The Nikkei was up 1.7 percent at 15,236.62 in midmorning trade, moving away from a 2-1/2 month low just below 15,000 set on Monday. It was still down more than 6 percent so far this year, underperforming many of its regional peers. "This is just an unwinding of risk-off trades. But the rebound is not that strong and it is unlikely to be sustainable," said Yasuo Sakuma, portfolio manager at Bayview Asset Management. "Looking at earnings so far, I can say that expectations had been higher (than the actual results). I doubt there will be any boost from earnings." Canon, Komatsu, Nintendo and Sumitomo Mitsui Financial Group are due to report earnings after the close on Wednesday. Traders said buying was driven by short covering by short-term players, while many investors remained cautious ahead of the U.S. Federal Reserve's meeting at which it is widely expected to trim its asset-buying programme by another $10 billion a month. "You cannot completely ignore the possibility that the Fed's decision could shake emerging markets again. So investors will be on the sidelines until the Fed's announcement," said Soichiro Monji, chief strategist at Daiwa SB Investments. "But I also think the market has priced in a $10 billion reduction in quantitative easing and that market sentiment will improve after the Fed's decision," he added. Like other share markets, the Nikkei had been under pressure in the past week on worries that a reduction in U.S. monetary stimulus and a slowdown in Chinese growth could hurt many emerging economies. Turkey's bold move to raise overnight rates by 425 basis points - and other rates by an even bigger amount - boosted the Turkish lira and raised hopes for stabilisation in many other emerging markets. The broader Topix index rose 1.9 percent, led by shares of financials, utilities and paper companies. Shares of Advantest, the world's largest maker of chip testing equipment, fell as much as 10 percent to their lowest since Oct. 9, after it widened its annual net loss forecast by 14 times due to weak demand for testers of chips used in smartphones. Nippon Electric Glass fell 2.4 percent and Asahi Glass also underperformed the overall market, staying almost flat, after U.S. rival Corning Inc warned that prices of LCD glass would decline further in the current quarter.