Poland on Sunday marked 85 years since the outbreak of World War II during annual commemoration ceremony held at dawn to remember Nazi Germany's first attacks that triggered the deadly conflict.

Nearly six million Poles died in the conflict that killed more than 50 million people overall, including the six million Jews who died in the Holocaust, half of them Polish.

The remembrance ceremony on Sunday was traditionally held in Westerplatte, on Poland's Baltic coast, where a Nazi German battleship had opened fire on a Polish fort 85 years ago to the day.

Speaking at Westerplatte, Prime Minister Donald Tusk said the lessons of World War II were "not an abstraction" and drew parallels with the war in neighbouring Ukraine.

"This war is coming again from the east," he said.

He urged NATO member states to be "fully devoted to defence... against the aggression that we are witnessing today on the battlefields of Ukraine".

Adolf Hitler's attacks on Poland led Britain and France to declare war on Nazi Germany. On 17 September, the Soviet Union in turn invaded Poland.

After the Nazis tore up their pact with Moscow, two alliances battled it out: the Axis powers led by Germany, Italy and Japan and the victorious Allied forces led by Britain, the Soviet Union and the United States.

Polish President Andrzej Duda took part in commemorations in the western Polish city of Wielun where Germany's first bombs fell 85 years ago.

Duda said "sorry" from Germany was not enough and called for reparations, adding: "This issue is not settled".

Although it has been 85 years since the war started, there are still unresolved matters according to Poland.

Poland's current pro-EU government led by Tusk has urged Germany to provide financial compensation over losses the country sustained at the hands of Nazi troops.

It echoed an earlier similar push by the populist Law and Justice (PiS) party that lost power in October election.

During his visit to commemorate the anniversary of the Warsaw Uprising, a doomed revolt against occupying forces, German President Frank-Walter Steinmeier spoke of plans to establish a memorial to the Polish victims of the Nazis.

"Many other efforts are underway, including for the remaining survivors of the German occupation. Our two governments are liaising closely on this," he said.

Steinmeier did not, however, provide any further details on the possible compensation measures.

According to Polish media, discussions between Warsaw and Berlin on financial compensation to the living victims of the Nazi Germany are underway, with Poland estimating up to 70,000 people would be eligible.