During the 1939 joint German-Soviet invasion of Poland, which started World War II, the town was captured by the Wehrmacht, which on 23 September handed it over to the Soviets, who occupied it until 23 June 1941, forcibly sending thousands to Siberia. In 1941–1944, the town was occupied by Nazi Germany. Germans murdered its Jewish minority, and in a nearby forest killed approximately 800 Poles. The Germans also operated a forced labour camp in the town. Bielsk was liberated by the Red Army on 30 July 1944, and then restored to Poland.