Gdansk Mayor Pawel Adamowicz said Poland was 'the first country in the world who stood in defence of freedom in Europe' and that it battled 'alone, deprived of help of allied forces', when it faced simultaneous attacks from Nazi Germany and Soviet Russia.

The ceremonies took place as the sun rose over the tall monument to the garrison's defenders, perched on a hill lined with wild roses and Polish flags.

The commemorations began with images of the war and Adolf Hitler projected over the monument, followed by the sounds of bombs and the Polish national anthem.

'This is the remembrance which we Poles do not want to use against anybody,' Prime Minister Donald Tusk said. 'We remember because we know those who will forget or falsify their history will bring disaster again.

'Long live the memory of those who died here, so we could live in a free Poland.'

Tusk is later expected to raise important questions in his meeting with Putin, including the 1940 Katyn massacre, during which Soviet security police killed about 4,000 Polish officers in the Katyn forest near Smolensk, Russia.

Relations have been tense between the Kremlin and Warsaw since Poland signed a deal with the US to host an American missile shield on its soil in exchange for a pledge of military aid. Russia has said the shield targets its nuclear arsenal despite US assurances that it is meant as protection against threats by countries like Iran.