NANJING -- One more survivor of the Nanjing Massacre passed away on Wednesday, reducing the number of living registered survivors to 21, the Memorial Hall of the Victims in Nanjing Massacre by Japanese Invaders said.

Massacre survivor Guan Shunhua died at the age of 101, according to the memorial hall in Nanjing, the capital of East China's Jiangsu province.

Guan was born in 1925. In 1937, her family fled to Huaian, which is north of Nanjing and also in Jiangsu, before the Japanese invading troops entered the then-Chinese capital.

The family returned to Nanjing a month later and took shelter in the refugee zone on Ninghai Road. Her uncle was killed by Japanese troops outside Zhongshan Gate.

The Nanjing Massacre took place after Japanese troops captured Nanjing on Dec 13, 1937. Over the course of six weeks, they proceeded to kill approximately 300,000 Chinese civilians and unarmed soldiers in one of the most barbaric episodes of WWII.

Over the years, the number of survivors who are able to share firsthand accounts of the massacre has continued to decline.

In 2014, China's top legislature designated Dec 13 as the national memorial day for the victims of the Nanjing Massacre. The Chinese government has also preserved survivors' testimonies, recorded via both written and video transcripts.

Documents related to the massacre were inscribed on UNESCO's Memory of the World Register in 2015.