Here is from the de-classified US Foreign Affair file #RG59-793.94/11631, from US Ambassador to Germany William Dodd at Berlin to Under-secretary of State Welles and Secretary of State Cordell Hull, dated Dec 14th, 1937. Click to read for yourself.
Note: The infamous Nanjing Massacre happened between Dec/13, 1937 to Feb 5, 1938 (the city fell on Dec 13). But this telegraph is dated Dec 14 1937, so the numbers are probably the sum of the civilians killed in the Shanghai up to the date Nanjing fell but not include those killed in Nanjing.
More discussion in Chinese here.