BEIJING—An official indicator of China’s manufacturing activity weakened for a second consecutive month in January, following outbreaks of domestic COVID-19 cases that affected the operations of some industries. The purchasing managers’ index, or PMI, for China’s manufacturing sector fell to 51.3 in January, down 0.6 percentage points from December 2020, according to data from the National Bureau of Statistics (NBS) on Sunday. Readings above 50 indicate expansion of the manufacturing industry, while a reading below it reflects a contraction. China has seen new virus clusters across the country, particularly in the north, and restrictions have been tightened to curb the spread. NBS senior statistician Zhao Qinghe said that locally transmitted coronavirus cases had affected the operations of certain industries, and that January is typically an off-season for factories due to the Lunar New Year holidays. Separately, the indicators for China’s service industry also dipped in January amid the local outbreaks. …