BEIJING (Reuters) - China's manufacturing activity grew faster than expected in September as factories cranked up production to take advantage of strong demand and high prices fuelled by a year-long building boom. The official Purchasing Managers' Index (PMI) released on Saturday stood at 52.4 in September, compared to 51.7 in August and well above the 50-point mark that separates growth from contraction on a monthly basis. That was the highest reading since April 2012. Analysts surveyed by Reuters had forecast the reading would come in at 51.5, easing marginally from August. China's long-ailing industrial sector is reporting its strongest earnings in years, fuelled by a government-led infrastructure spending spree, stronger factory-gate prices and a recovery in exports. The economy grew by a faster-than-expected 6.9 percent in the first half of 2017, and looks set to easily meet the government's full-year target of around 6.5 percent. (Reporting by Elias Glenn; Editing by Richard Pullin)