NANJING, June 11 -- China is applying to UNESCO to list 11 sets of documents relating to the 1937 Nanjing Massacre on the Memory of the World Register.

The documents are first-hand materials that recorded the massacre, and are of historical importance, said Zhu Chengshan, curator of the memorial hall of the victims, on Wednesday.

Preparation work began in 2009, and the application process started in March this year, when the State Archives Administration handed the documents to the Memory of the World secretariat, according to Zhu, who initiated the application.

The documents, which include diaries, films, photographs and testimonies, depict the brutality of Japanese invaders in the massacre, Zhu told Xinhua.

"These documents truthfully record the atrocities," Zhu said.

On Tuesday, Foreign Ministry spokeswoman Hua Chunying confirmed that China had applied to UNESCO to list documents relating to the massacre and Japan's wartime sex slaves, so-called "comfort women", on the Memory of the World Register.

Created in 1997, the register protects documentary heritage.

Historians estimate that 200,000 women were forced into sexual servitude by Japanese forces during WWII, most of them from countries invaded by Japan at that time.