BEIJING, May 31 (Reuters) - China’s factory activity expanded at a slightly slower-than-expected pace in May, as surging raw material prices weighed on industrial production. The official manufacturing Purchasing Manager’s Index (PMI) fell to 51.0 in May, data from the National Bureau of Statistics (NBS) showed on Monday, remaining above the 50-point mark that separates growth from contraction. Analysts had expected a PMI reading of 51.1 in May, unchanged from April. China’s economy expanded a record 18.3% in the first quarter of 2021, but the pace of growth slowed in April, the NBS said previously. Supply bottlenecks and rising raw material costs weighed on production that month. Reporting by Colin Qian and Gabriel Crossley; Editing by Ana Nicolaci da Costa Our Standards: The Thomson Reuters Trust Principles.