SHANGHAI/BEIJING (Reuters) – Chinese stock markets tumbled for a second straight day on Wednesday as investors crowded the exits, fearing a government campaign to prop up share prices was faltering and unnerved by a steady stream of gloomy economic news. On Wednesday, the Commerce Ministry added to those concerns, saying exports could continue falling in coming months, after an 8.3 percent plunge in July, their biggest drop in four months. Domestic and global investors are growing anxious that China’s economy will suffer a hard landing.