BEIJING (AP) — The southern Chinese city of Guangzhou has shut down a neighborhood and ordered residents to stay home for door-to-door coronavirus testing following an upsurge in infections that has rattled authorities. Guangzhou, a business and industrial center of 15 million people north of Hong Kong, has reported 20 new infections over the past week. The number is small compared with India’s thousands of daily cases but alarmed Chinese authorities who believed they had the disease under control. Outdoor markets, child care centers and entertainment venues were closed. Indoor restaurant dining was prohibited. Grade schools were told to stop in-person classes. People in parts of four nearby districts were ordered to limit outdoor activity.