BEIJING: Hundreds of thousands more people were ordered to stay home in northern China Tuesday, joining millions under strict lockdown as authorities raced to contain a surge in Covid cases that have reached a 21-month high. China — where the virus emerged two years ago — has followed a “zero-Covid” strategy of tight border restrictions, lengthy quarantines and targeted lockdowns as Beijing prepares to welcome thousands of overseas visitors to February’s Winter Olympics. But authorities have faced a resurgent virus in recent weeks, reporting 209 infections on Tuesday — the highest single-day t…