Candles flickered in the darkening winter gloom of the sprawling site, which Israeli President Moshe Katsav called "the capital of the kingdom of death."
During World War II, 1.5 million people -- mostly Jews -- were killed at the site. Others who perished there included Soviet prisoners of war, Poles, Gypsies, Jehovah's Witnesses, homosexuals and political opponents of the Nazis.
The haunting commemoration was held at the place where new arrivals stumbled out of cattle cars and were met by Nazi doctors who chose a few to be worked to death while the rest were sent immediately to gas chambers. Others died of starvation, exhaustion, beatings and disease.
"It seems if you listen hard enough, you can still hear the outcry of horror of the murdered people," Katsav said. "When I walk the ground of the concentration camps, I fear that I am walking on the ashes of the victims."
As night fell and the ceremony ended with a locomotive whistle blaring over loudspeakers, a half-mile of train tracks leading from the front gate to the crematoriums were set ablaze in a pyrotechnic display -- two flaming rails amid the snow.
The 30 leaders, including Vice President Dick Cheney, Presidents Aleksander Kwasniewski of Poland, Vladimir Putin of Russia, and Jacques Chirac of France, placed candles shielded in blue lanterns on a low stone memorial. Soldiers of a Polish honor guard stood stiffly in the freezing wind. New Ukrainian President Viktor Yushchenko gently set down his candle and made the sign of the cross.
Germany's President Horst Koehler placed a candle but didn't speak, in recognition of his country's responsibility for the Holocaust, Adolf Hitler's attempt to wipe out Europe's Jews. In all, some 6 million Jews died in Hitler's network of camps, while several million non-Jews also perished.
Soviet troops liberated Auschwitz and neighboring Birkenau -- the occupiers' names for Polish Oswiecim and Brzezinka -- on Jan. 27, 1945.
At the ceremony, young girls brought blankets to survivors sitting in the cold.
Auschwitz survivor Gabi Neumann, 68, traveled from his home in Israel and held up a poster that bore the words, "Stop it before it happens again" and the yellow stars of the European Union flag distorted to resemble a swastika.
"I made this poster because anti-Semitism is a big problem in Europe," said Neumann, who was an 8-year-old boy when he was freed from the camp. Originally from Slovakia, he lost a grandmother at Auschwitz.
"But she has no grave," he said. "I am happy there is snow here because it keeps me from standing on her ashes."
Putin compared the Nazis with modern terrorists.
"Today we shall not only remember the past but also be aware of all the threats of the modern world," he said. "Terrorism is among them, and it is no less dangerous and cunning than fascism."
Earlier in Krakow, Cheney noted that the Holocaust did not happen in some far-off place but "in the heart of the civilized world."
"The story of the camps shows that evil is real and must be called by its name and must be confronted," he said.
People at the ceremony expressed concern over recent incidents such as a walkout from an Auschwitz commemoration by far-right local legislators in Germany, and a statement from far-right National Front leader Jean-Marie Le Pen in France, who minimized the brutality of Nazi rule during the occupation by German troops. He said it "was not particularly inhuman, even if there were a few blunders."
Camp survivor Franczisek Jozefiak, 80, said the world still needed reminding.
"Today I'm remembering my father, gassed here. I'm remembering the atrocious things they did to us here," said Jozefiak, who is from Krakow.
The Nazi guards lined them up and told some to go right, others left, he said. Jozefiak went left and his father went right and was taken to the gas chamber.
"The message today is: No more Auschwitz," he said. "But the world has learned nothing so far -- you see they are fighting and killing each other everywhere in the world.
"Today they are saying a lot because of the anniversary, but tomorrow they will forget," he said.