Auschwitz 70th anniversary: Survivors mark camp liberation
The commemoration will be held at the site in southern Poland where 1.1 million people, the vast majority Jews, were killed between 1940 and 1945.
It is expected to be the last major anniversary event that survivors are able to attend in considerable numbers.
Heads of state and representatives from wartime Allies will also be present.
Events include the laying of a wreath, a church service, and the lighting of candles at a memorial in the former death camp of Birkenau, which was part of the Auschwitz complex.
Auschwitz-Birkenau was liberated by the Red Army of the Soviet Union on 27 January 1945. It opened as a museum in 1947.Renee Salt, 85, from north London, is among the survivors travelling to Tuesday's commemoration.
She visited the camp for the first time 10 years ago and "buried the ghosts", she told the BBC, and has been going back ever since.
"I'll do it for as long as I can. Why? There are still a lot of Holocaust deniers, the world over, and if we don't speak out, the world won't know what happened."
At the scene: Kevin Connolly, BBC News
Those who survived Auschwitz lived through one of the 20th Century's worst acts of hatred and inhumanity. Many of those still alive today were children in 1945, but they are elderly now and this may be the last significant anniversary where so many will gather.
A huge, white temporary building has been erected over the brick railway buildings where many of the Jews of Europe were sorted into those who were fit enough for slave labour and those who would be taken straight to the gas chambers.
Candles have been lit at the Death Wall where prisoners were executed - small points of light in this wintry landscape of snow and ice, where Europe is remembering a time of darkness.
On Tuesday the Russian defence ministry published what it said were archive documents about the liberation of Auschwitz.
They include an account by Gen Kramnikov of the 60th Army of the First Ukrainian Front, whose soldiers opened the gates, about "endless crowds of people" leaving the death camp.
"They all look extremely exhausted, grey-haired old men, youths, women with young babies and teenagers, nearly all of them half-naked," the general wrote.
"The first indications are that in Auschwitz hundreds of thousands of prisoners have been worked to death, burned or shot dead."German President Joachim Gauck and French President Francois Hollande are among the national leaders travelling to Poland for the anniversary.
But Russian President Vladimir Putin is not attending, amid a row with Poland over the commemoration and linked to Russia's recent intervention in Ukraine.
Before leaving Paris, Mr Hollande condemned the "unbearable" problem of contemporary anti-Semitism, telling Jews at a Holocaust memorial: "France is your homeland."
He spoke after a Jewish group said the number of anti-Semitic acts recorded in France had doubled in 2014 to more than 850. Earlier this month, a Jewish supermarket was targeted during deadly attacks that shook the French capital.
On the eve of the Auschwitz anniversary, German Chancellor Angela Merkel said it was a "disgrace" that Jews faced insults, threats and violence.
"We've got to fight anti-Semitism and all racism from the outset," she said at a memorial event in Berlin. "We've got to constantly be on guard to protect our freedom, democracy and rule of law."
The museum has long struggled to find funding for its upkeep, though the Auschwitz-Birkenau Foundation recently said it had almost reached its goal of raising an endowment of more than $150m (£100m).
