Activity in China’s mammoth factory sector edged up to a four-month high in February but export orders shrank at their fastest rate in 20 months, a private survey showed, painting a murky outlook that argues for more policy support. While domestic demand picked up slightly, the new export orders sub-index shed three hefty points from January to skid to 47.1, the sharpest rate of contraction since June 2013. “Domestic economic activity is likely to remain sluggish and external demand looks uncertain,” said Qu Hongbin, HSBC’s chief economist in China.