Missionaries were active in Nanking from 1843 and there was quite a number of Christians in Nanking by 1937 and the Japanese massacre was about 6 weeks
The Opium War and Foreign Encroachment | Asia for Educators | Columbia University
Along with India, China was another early mission of the Foreign Christian Missionary Society. In 1886 it sponsored Canadian Dr. William Macklin (1860-1947) as a missionary to Nanking. Edwin P. Hearnden (d. 1896) and Albert F.H. Saw (1865-1898) from Britain soon joined the mission along with two couples from the United States. They began medical work, schools, and other mission stations assisted by converts like Shi Kwei-biao (d.1925) and additional missionaries like Rosa Tonkin from Australian Churches of Christ. These missions persevered under Chinese opposition to "foreign" influences, through the Boxer Uprising of 1898-1901, and during Sun Yat-sen's republican revolution of 1911-1912. By the 1920's the missionaries began to relinquish control to Chinese Christian leaders like Li Hou-fu (d.1939) the co-secretary of the mission.
Chinese leadership was essential in preserving the churches through the trying political situation of the next few decades. Japanese occupation of China began in 1937 with the brutal occupation of Nanking where missionaries Miner Searle Bates (1897-1978) and Minnie Vautrin (1886-1941) protected thousands of innocent lives. During the occupation, Shao Ching-San (d. 1958), known as Luther Shao, who completed a Ph.D. at Yale in 1934, returned to China and became secretary of the mission. Due to Communist rule beginning in 1949 the last of the United Christian Missionary Society workers left in 1951
World Convention » China