Prime Minister Mateusz Morawiecki took part in commemorations in Wieluń, the first Polish city to be bombed by the Germans at 4:40 am on September 1, 1939.
Meanwhile, President Andrzej Duda, along with officials including Defence Minister Mariusz Błaszczak, took part in ceremonies on the Westerplatte peninsula in the northern city of Gdańsk.
'Lesson in history that must not be forgotten'
Addressing those gathered in Wieluń, the Polish prime minister said that his country was "the guardian of the memory" of World War II amid attempts by some to rewrite history and "blur the truth about the war."
He added that remembering the events of 81 years ago was important because they were "a lesson in history that must not be forgotten."
The first bombs of World War II fell on a hospital in Wieluń, killing 32 people, including 26 patients. In all, the Germans killed around 1,200 in the city that day, according to estimates.
Wieluń, in central Poland, was located close to the Polish-German border before national boundaries shifted after the war.
Prime Minister Mateusz Morawiecki speaks at the commemorative event in Wieluń, central Poland. Photo: PAP/Grzegorz Michałowski
The Gdańsk commemoration, meanwhile, traditionally started at 4:45 am, the time on September 1, 1939 that the German battleship Schleswig-Holstein began shelling a Polish military depot on Westerplatte in the first battle between Polish and German soldiers of WWII.
Sirens wailed and the Polish national anthem was played at a monument honouring those who defended the Polish coast.
The week-long defence by the Poles against overwhelmingly larger German forces became a symbol of the heroism of Polish soldiers.
'Warning to the world'
During the ceremony, the Polish president said that Westerplatte was "a warning to the world ... that such events should never happen again."
He noted that the German forces could not break the defenders' resistance for a week even though they were far more numerous.
"Exactly 81 years ago, on September 1, 1939, World War II broke out after Nazi Germany invaded Poland," Duda said.
President Andrzej Duda attends the commemorations at Westerplatte on Tuesday. Photo: PAP/Adam Warżawa
Almost 6 million Polish citizens, including 3 million Polish Jews, lost their lives in World War II, officials said in marking the anniversary.
The country emerged from the war completely destroyed and looted, and its economy lay in ruins, they added.
Source: IAR, PAP
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