Sirens blared and thousands of doves were released yesterday as Chinese President Xi Jinping presided over a sombre ceremony in Nanjing marking 80 years since the wartime massacre in the city by Japanese troops.  According to China, 300,000 civilians and soldiers were killed in a frenzy of murder, torture, rape, arson and looting in the six weeks after invading Japanese troops seized Nanjing, then the capital city, on December 13, 1937.