BEIJING—An official gauge of manufacturing activity in China rose faster than expected in February, making for a strong start to 2017, as demand picked up and stimulus momentum continued.

China’s official manufacturing purchasing managers index increased to 51.6 from 51.3 in January, the National Bureau of Statistics said Wednesday. The February reading beat a median forecast of 51.3 by 10 economists polled by The Wall Street Journal. The index has been above the 50 mark separating expansion from contraction for seven consecutive...