A second Chinese manufacturing gauge for September was below most economists’ estimates, casting doubt on the strength of a rebound from a two-quarter economic slowdown.

The Purchasing Managers’ Index was at 51.1, the National Bureau of Statistics and China Federation of Logistics and Purchasing said Tuesday in Beijing. That compares with 51 in August and the 51.6 median estimate in a Bloomberg News survey.

Premier Li Keqiang is trying to protect a targeted 7.5 percent expansion for 2013 while limiting additional stimulus as the Communist Party tries to restructure the economy away from dependence on exports and investment. Tuesday’s report came after a manufacturing gauge released Monday by HSBC Holdings Plc and Markit Economics unexpectedly weakened from a preliminary reading.

Estimates for Tuesday’s index from 30 economists ranged from 51 to 52.2. Levels above 50 signal expansion.

The statistics bureau reports third-quarter gross domestic product on Oct. 18. The economy probably grew 7.7 percent from a year earlier, according to a Bloomberg News survey of analysts, up from the second quarter’s 7.5 percent pace.