Flags flew at half staff, public entertainment was canceled and 1.3 billion people were asked to observe three minutes of silence Monday as China began three days of mourning for victims of the country's massive earthquake. Officials asked for the horns of cars, trains and ships and air raid sirens to sound as people fall silent at 2:28 p.m. - exactly one week after the quake splintered thousands of buildings and killed an estimated 50,000 people. The Olympic torch relay - a potent symbol of national pride in the countdown to August's much anticipated Beijing games - also was suspended during the mourning period. The national flag in Tiananmen Square, which is raised in a solemn ceremony every morning at dawn, fluttered at half-mast. The mourning period begins as hope of finding more trapped survivors dwindled, and preventing hunger and disease among the homeless became more pressing.