China's factory activity grows at fastest pace since March, private PMI shows

* RatingDog manufacturing PMI 51.2 in Sept vs 50.5 in August * New export orders expand for the 1st time since March * Input cost inflation highest in 10 months; output prices fall By Ellen Zhang and Ryan Woo BEIJING, Sept 30 (Reuters) – China's factory activity in September expanded at the quickest pace since March, as rising new orders drove faster production growth, a private-sector survey showed on Tuesday. The RatingDog China General Manufacturing Purchasing Managers Index (PMI), compiled by S&P Global, rose to 51.2 in September from 50.5 in August, beating analysts' expectations of 50.2 in a Reuters poll. The 50-mark separates growth from contraction. The reading was better than that of an official survey released earlier on Tuesday, which showed factory activity extending declines f