Commemorations are planned across the country, including in the town of Wieluń, which was the first to be bombed by the Germans at 4:40 a.m. on September 1, 1939.
The first bombs of World War II fell on a hospital in Wieluń, killing 32 people, including 26 patients, according to historical records.
In all, the Germans killed around 1,200 in the city that day, according to estimates.
Wieluń, in south-central Poland, was located close to the Polish-German border before national boundaries shifted after the war.
Ceremonies will also be held on the Westerplatte peninsula in the northern city of Gdańsk, where the German battleship Schleswig-Holstein at 4:45 a.m. on September 1, 1939 began shelling a Polish military depot in the first battle of WWII.
State and local government leaders, including Gdańsk Mayor Aleksandra Dulkiewicz are expected to gather for a memorial ceremony near a monument honouring those who defended the Polish coast.
Polish President Andrzej Duda said last year that the defence of Westerplatte by the Poles against overwhelmingly larger German forces in the early days of WWII became a symbol of "the extraordinary heroism" and patriotism of Polish soldiers.
He noted that the German forces could not break the defenders' resistance for a week even though they were far more numerous.
Almost 6 million Polish citizens, including 3 million Polish Jews, lost their lives in World War II, officials said in marking the upcoming anniversary.
The country emerged from the war completely destroyed and looted, and its economy lay in ruins, they added.
(gs)
Source: IAR, PAP