BEIJING—Two key gauges of Chinese factory output registered a pickup in March on signs that policies aimed at boosting growth were having some impact.

China’s official manufacturing purchasing managers index increased to 50.2 last month month from 49.0 in February, according to the National Bureau of Statistics. This is the first time in eight months the figure has been at or above 50, the level dividing expansion from contraction. A separate indicator, the private Caixin manufacturing PMI, rose to 49.7 in March from 48.0...