On September 1, 1939, the first day of the German invasion of Poland and World War II, there was a skirmish between German saboteurs and the Polish self-defense in the present-day district of Michałkowice. German saboteurs then entered the local mine, taking several dozen Polish miners as hostages. After a battle, Polish troops and volunteers, including members of the "Sokół" Polish Gymnastic Society and boy scouts, recaptured the mine. There were deaths on both sides, and the Poles also captured dozens of German saboteurs. The Germans eventually invaded and captured the city in the following days, and already on September 8, 1939, the German "Freikorps" murdered six Poles in the city. In September 1939, the German "Einsatzgruppe I" operated in the city and committed various crimes against the Polish population. During the German occupation, two forced labour camps were established and operated in the city: one for Poles ("Polenlager") and one for Jews. In April 1944, the Germans also established a subcamp of the Auschwitz concentration camp, in which over 900 people were held and subjected to forced labour. In January 1945, the prisoners of the subcamp were taken to the Mauthausen concentration camp, and shortly afterwards the Germans left the city and the occupation ended.