After the joint German-Soviet invasion of Poland, which started World War II in September 1939, the town was occupied by Germany, which carried out a genocidal campaign against the local Polish and Jewish population. Chełmża was one of the sites of executions of Poles carried out by Germany in 1939 as part of the "Intelligenzaktion". Many local Poles, especially teachers, were also massacred in the Barbarka forest in present-day Toruń, also as part of the "Intelligenzaktion". The German state at the time considered Poles and Jews to be "untermenschen" and planned their eradication as national groups. To escape this fate many local Poles took the III and IV group of Volksliste. In early 1945, in Chełmża, Polish forced labourers evacuated from Jajkowo were forcibly conscripted by the Germans to the Organisation Todt, however, some managed to escape. As result of German extermination and repressions the population of the town declined to 10,000 in March 1945.