In Warsaw, the flag was hoisted on the Royal Castle's Clock Tower. The president was accompanied by his wife, Agata Kornhauser-Duda and a range of top officials.
In Szczecin, the national colours were hoisted on the Province Office building.
Poland marks National Flag Day and the Day of the Polish Diaspora and Poles Abroad on May 2.
Later in the day, the president spoke in front of the Belvedere Palace in Warsaw after he presented state distinctions to people who had made special contributions to the Polish diaspora and promoted Polish culture and history.
"The flag has its joining force, its uniting power, a power that builds the community," the president said, adding that the national flag gained particular significance in foreign countries where "so many of our compatriots emigrated to, especially in the past two centuries."
PM Mateusz Morawiecki said that "the white-and-red colours, our flag, is the past, the present and the future." The prime minister recalled that originally, the Polish army's colour was crimson, which was regarded as the noblest colour. "We are this bravest, noblest nation," he said.
Historically, the Polish national colours derive from the Kingdom of Poland's and the Grand Duchy of Lithuania's coats of arms, with both the Polish eagle and the Lithuanian mounted knight presented in white and set against red backgrounds. (PAP)
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