The heads of state of Poland and Germany are marking 80 years since the outbreak of history's bloodiest conflict with a ceremony in the Polish city of Wielun, where the first World War II bombs fell.
In an early morning ceremony on Sunday German President Frank-Walter Steinmeier asked Poland's forgiveness.
"I bow my head before the victims of the attack on Wielun. I bow my head before the Polish victims of Germany's tyranny. And I ask forgiveness," Steinmeier said in both German and Polish.
Polish President Andrzej Duda and President Steinmeier will deliver speeches in the small central city to remember the war that killed more than 50 million people, including six million Jews in the Holocaust.
"I saw dead bodies, the wounded... Smoke, noise, explosions. Everything was burning," Wielun bombing survivor Tadeusz Sierandt, 88, told AFP ahead of the anniversary.
The carpet-bombing came one week after Germany and the Soviet Union secretly agreed to carve up Eastern Europe between them by signing the Molotov-Ribbentrop Pact.
Polish Prime Minister Mateusz Morawiecki and European Commission Vice President Frans Timmermans will attend a dawn remembrance Sunday in Westerplatte, where a Nazi German battleship opened fire on a Polish fort on September 1, 1939.
Malta's President George Vella is also attending.
Hitler's attacks on Poland led Britain and France to declare war on Nazi Germany. On September 17, the Soviet Union in turn invaded Poland.
After the Nazis tore up the pact with Moscow, two alliances battled it out to the end: the Axis powers led by Germany, Italy and Japan and the victorious Allied forces led by Britain, the Soviet Union and the United States.
Later Sunday, US Vice President Mike Pence, Steinmeier and Duda will deliver speeches at a ceremony in Warsaw's Pilsudski Square, the site of the Tomb of the Unknown Soldier.
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Poland suffered some of the worst horrors of World War II: nearly six million Poles -- half of them Jews -- died in the conflict.
Though it has been 80 years since the war started, there are still unresolved matters according to Poland, which says Germany owes it war reparations.
A parliamentary commission is currently working on a new analysis of the extent of Poland's wartime human and material losses. Berlin, however, believes the case is closed.
German Chancellor Angela Merkel will attend the Warsaw ceremony, but no other major world leaders are expected.
US President Donald Trump had planned to attend the war commemorations but cancelled at the last minute so that he could monitor Hurricane Dorian.
Also not coming are French President Emmanuel Macron and British Prime Minister Boris Johnson, while Russian President Vladimir Putin was not invited -- unlike 10 years ago -- because of Moscow's 2014 annexation of Crimea from Ukraine.
The Polish presidency has said it expects around 40 foreign delegations to attend, a few of them led by heads of state.
They include Ukrainian President Volodymyr Zelensky whose partnership matters to Poland, which believes its security depends on Ukraine remaining outside of Russia's sphere of influence.
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Duda said Poland wants neighbour "Ukraine to be closer to the European Union, to be closer to NATO" after meeting with Zelensky in Warsaw on Saturday.
Zelensky for his part slammed the controversial Nord Stream 2 pipeline set to send Russian gas to Germany as a "threat" to Europe.
The US, Poland and Ukraine agreed later Saturday to beef up cooperation aimed at securing energy supplies in the region reliant on Russian deliveries.
The agreement is largely focused on gearing Ukraine's gas infrastructure to deliveries from the West, including US liquefied natural gas (LNG).
While in town, Pence hopes to sign a pact with Poland on confronting 5G network risks, according to a senior US administration official who spoke on condition of anonymity.
The United States is pressing allies, with mixed success, to reject Chinese 5G technology, especially from the giant mobile phone company Huawei.
Washington fears that Huawei will provide Beijing with a way to spy on communications from the countries that use its products and services.