* HP jumps after outlook
* China manufacturing data shows contraction
* Futures off: Dow 103 pts, S&P 13.4 pts, Nasdaq 24.75 pts
By Chuck Mikolajczak
NEW YORK, May 23 (Reuters) - U.S. stock index futures fell on Thursday, putting the S&P 500 on track for its first daily back-to-back declines in a month, amid investor concerns the U.S. Federal Reserve may begin to taper its stimulus measures and over weak data in China.
* The S&P 500 posted its biggest decline in three weeks on Wednesday, after minutes from the latest U.S. Federal Reserve meeting showed some officials were open to tapering large-scale asset purchases as early as at the June meeting.
* The minutes came in the wake of comments earlier in the session by Fed Chairman Ben Bernanke, who said the Fed could scale back the pace of bond purchases at one of the "next few meetings" if the economic recovery looked set to maintain forward momentum.
* Adding to selling pressure, China's flash HSBC Purchasing Managers' Index for May fell to 49.6, slipping under the 50-point level which indicates expansion for the first time since October, raising concerns the recovery in the world's second-largest economy has stalled and a sharper downturn may be on the horizon.
* The benchmark S&P index has jumped 16.1 percent since the start of the year, boosted by slowly improving U.S. economic data and stimulus measures by central banks around the globe.
* S&P 500 futures dropped 13.4 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 103 points, and Nasdaq 100 futures slumped 24.75 points.
* Hewlett-Packard Co jumped 11.6 percent to $23.69 in premarket trade after the computer maker raised its 2013 earnings outlook after quarterly results beat low expectations.
* Title insurer Fidelity National Financial Inc and buyout firm Thomas H. Lee Partners are in advanced talks to acquire mortgage service provider Lender Processing Services Inc , a source familiar with the matter said.
* European and Asian shares dropped and the Euro STOXX 50 Volatility Index surged 18 percent to a 3-week high, spooked by concerns about the future of the Fed's stimulus program and compounded by weak economic data from China.