Asian stocks and emerging market currencies tumbled on Wednesday and commodities fell after China allowed the yuan to fall sharply for a second straight day, forcing investors to seek refuge in safe-haven government debt. On Wednesday, the People’s Bank of China (CNY=CFXS) set the yuan’s midpoint rate (CNY=SAEC) weaker than Tuesday’s closing market rate, which had already fallen sharply after China devalued its currency by 2 percent in a surprise move.