South Korea's factory activity grew in September at the strongest pace in four months, as export demand hit the fastest pace in 15-1/2 years led by the chip and auto sectors, a survey showed on Thursday. • The purchasing managers index (PMI), published by S&P Global, stood at 53.9 in September, up from 52.3 in August and the highest since May. The index remained above the 50 mark separating expansion from contraction for a 10th consecutive month.