The Polish and Israeli presidents visited Treblinka on Monday
The Polish and Israeli presidents have led events to mark the 65th anniversary of the Warsaw Ghetto Uprising.
The main ceremony was held at a monument honouring hundreds of Jewish fighters who resisted German attempts to eradicate the ghetto.
Polish President Lech Kaczynski said the world must remain vigilant to prevent a repeat of such horrors.
Israeli President Shimon Peres said that the fighters represented the victory of humanity over bestiality.
The uprising was the largest act of Jewish resistance in the Holocaust.
During the ceremony, a Jewish cantor sang a memorial prayer to the victims, and wreaths were laid at the foot of the monument.
Several hundred people were present, including Holocaust survivors, politicians and members of the public.
Mr Peres, who began a four-day visit on Monday with a trip to the Treblinka site in north-east Poland, praised the heroism of the Jewish fighters.
"The majority of the uprising fighters died, murdered in cold blood," he said.
They lost the battle, but from history's point of view, there never was a greater victory. A victory of men over human bestiality, of pure souls over fallen ones."
The annual commemoration of the uprising is normally held on 19 April but was brought forward to avoid clashing with the Jewish Sabbath.
For nearly a month in 1943, several hundred Jews, armed with pistols and home-made bombs, held off the German army for almost a month before the ghetto was razed to the ground.
By that time, the Nazis had sent 300,000 Jewish residents of the ghetto to the gas chambers at the Treblinka death camp.
The first clashes occurred at the start of 1943 as residents took up arms to prevent more Jews being sent to the camp.
The full-scale uprising began in April in response to Nazi plans to wipe out the 60,000 remaining inhabitants.
Thousands of Jews died in the fighting as Nazi troops resorted to explosives to destroy the ghetto the German occupiers had created in 1940.
A candle-lighting ceremony will also take place at the site of the bunker where the leader of the uprising, Mordechai Anielewicz, and 80 followers killed themselves as Nazi forces suppressed the uprising.
Jewish residents fought for nearly a month before the uprising was crushed
The BBC's Adam Easton says Poland's Jewish community - numbering more than three million - used to be the largest in Europe, but was almost completely wiped out in the Holocaust.
But Polish Chief Rabbi Michael Schudrich says there is growing interest in the country's Jewish past.
"In Poland anti-Semitism is no greater than the unacceptable level of France or England," he said.
"In addition, we are finding more and more Poles who want to work with us in preserving these cemeteries and synagogues and Jewish memory.
"There are more Jewish festivals in Poland today than I believe any other country in the world".
The Polish government also plans to compensate people whose property was stolen by the Nazis and the subsequent communist administrations.