U.S. stock index futures point to a lower open Wednesday as investors await a raft of economic data including the publication of the national employment report from ADP and the Federal Reserve’s Beige Book offering a window into regional economic conditions.

Futures on the Dow Jones Industrial Average were down 0.26 percent, futures on the Standard & Poor's 500 Index were down 0.18 percent and those on the Nasdaq 100 index were down 0.16 percent.

Investors will assess the ADP National Employment Report, which is a precursor to the closely watched government employment report due at the end of the week. The ADP report, which measures the monthly change in nonfarm private employment, is due to be released at 8:15 a.m. EDT. Analysts polled by Thomson Reuters are estimating private payrolls to rise by 165,000 in May after increasing 119,000 in April.

“Recent employment related data has been mixed with consumers reporting a more upbeat outlook on the job market, while private sector surveys suggested easing employment in May. Our current forecast for nonfarm payrolls is for a 150K gain, but we will revisit this if the ADP Report comes in markedly different from expectations,” a note from Credit Agricole said.

Investors are also expected to focus on the Institute for Supply Management’s non-manufacturing Purchasing Managers’ Index, also known as ISM Services PMI, and the Commerce Department's factory orders report for the month of April to be released after the opening bell on Wednesday.

Analysts polled by Thomson Reuters expect the Services PMI to rise to 53.5 in May from 53.1 in April and the factory orders to post a 1.5 percent increase in April after declining 4.9 percent in the prior month.

In addition, the Federal Reserve's Beige Book, a compendium of economic reports from the central bank’s twelve districts, is scheduled to be released at 2 p.m. EDT and will give a picture of economic trends and challenges faced by the country. The report is likely to show that the world’s largest economy expanded at a moderate pace in the April-May period.

European stock markets declined in early trading on Wednesday as investors await economic data from across the EU and the U.S. London’s FTSE 100 was down 0.62 percent, Germany's DAX-30 declined 0.42 percent and France's CAC-40 fell 0.53 percent.

Asian stock markets plunged to their lowest level in 2013, on Wednesday, as comments from two Fed officials added to concerns that the Fed might start to scale down its massive stimulus program sooner rather than later.

"Wariness over an exit from the Fed stimulus is driving Asian shares lower on worries that the ample money invested here could flee, although an improving U.S. economy should be seen as positive for many export-reliant Asian economies," Hirokazu Yuihama, a senior strategist at Daiwa Securities in Tokyo, told Reuters.

Japan’s Nikkei plunged 3.83 percent, Hong Kong’s Hang Seng declined 0.97 percent and China’s Shanghai Composite fell 0.07 percent, while South Korea’s KOSPI Composite declined 1.52 percent and India’s BSE Sensex was trading flat in late afternoon trade.