U.S. labor markets were tight enough to fuel small wage gains in some professions in recent weeks, though some companies already were feeling a chill from an economic slowdown in China, the Federal Reserve said on Wednesday. Overall, U.S. economic activity continued to expand across most regions and sectors from July to mid-August, the Fed said in its Beige Book report of anecdotal information on business activity collected from contacts nationwide. The combination of a healing labor market and worries about Chinese economic growth underscored the challenge faced by the U.S.