The reported move is seen as the latest step by Beijing to broaden its efforts to raise awareness of Japan's wartime aggression at a time when Tokyo's relations with its neighbors, especially Beijing and Seoul, have plunged to one of their lowest points in many years over their shared history and territorial disputes.
Unit 731 was the Japanese Imperial Army's covert biological and chemical warfare research and development unit, which carried out brutal and often fatal experiments on prisoners of war. Historians say the unit, based in Harbin, held prisoners from China, Korea and the Soviet Union.
According to the report by Harbin-based newspaper Life Daily (Shenghuo Bao), the Unit 731 Criminal Evidence Museum will build an annex this year to exhibit 1,740 pieces of new documents and relevant pieces of evidence on atrocities by the Japanese unit.
Such new exhibits have been collected over the past two years, the report said.
The museum, which sits where the Japanese unit had once stood, was opened to serve as a reminder of the heinous crimes by Japan during the war.
Japan has not officially acknowledged the atrocities of Unit 731.