China's Jilin Provincial Archives has released a letter written by a Japanese citizen who lived in China in 1941.
It says that some 20 Korean women were forced at the time to serve at a comfort station in the Japanese army compound stationed in northern China.
A separate document written by the Japanese military police in Nanjing described 36 Korean women at a military brothel during World War Two as "special comfort women," which indicates that they were coerced into sexual servitude.
These and 23 other documents were released by the Chinese archives administration through Korean media on Monday.
Local experts say the set of rare evidence is more proof that Japan forcefully mobilized Korean females as comfort women under the 1938 National Mobilization Law.
The Korean government has pressed Japan for decades to make a formal apology and provide compensation to the wartime victims, but Japan has refused.
Historians say up to 200-thousand women from Korea, China and other Asian nations were coerced into sexual servitude at Japanese brothels during the war.
Sohn Jung-in, Arirang News.