A piercing air raid siren is heard to mourn victims at a ceremony for the National Memorial Day for Nanjing Massacre Victims held in Nanjing, capital of East China's Jiangsu province, Dec 13, 2020. (Photos: China Daily)

China's national flag flies at half-mast to mourn victims at a ceremony for the National Memorial Day for Nanjing Massacre Victims held in Nanjing, capital of East China's Jiangsu province, Dec 13, 2020.

A piercing air raid siren is heard to mourn victims at a ceremony for the National Memorial Day for Nanjing Massacre Victims held in Nanjing, capital of East China's Jiangsu province, Dec 13, 2020.

People mourn for victims at a ceremony for the National Memorial Day for Nanjing Massacre Victims held in Nanjing, capital of East China's Jiangsu province, Dec 13, 2020.

People mourn for victims at a ceremony for the National Memorial Day for Nanjing Massacre Victims held in Nanjing, capital of East China's Jiangsu province, Dec 13, 2020.

A piercing air raid siren is heard to mourn victims at a ceremony for the National Memorial Day for Nanjing Massacre Victims held in Nanjing, capital of East China's Jiangsu province, Dec 13, 2020.

People mourn for victims at a ceremony for the National Memorial Day for Nanjing Massacre Victims held in Nanjing, capital of East China's Jiangsu province, Dec 13, 2020.

A ceremony for the National Memorial Day for Nanjing Massacre Victims is held in Nanjing, capital of East China's Jiangsu province, Dec 13, 2020.

A ceremony for the National Memorial Day for Nanjing Massacre Victims is held in Nanjing, capital of East China's Jiangsu province, Dec 13, 2020.