Oswiecim (Poland) (AFP) - Stony-faced and dressed in black, Germany's chancellor walked in silence along the railway tracks that brought prisoners to the Auschwitz-Birkenau Nazi death camp.

She paused in front of one of the cattle trucks used to transport people to the camp in then occupied Poland where 1.1 million people were killed.

On the historic visit, her first as chancellor, a visibly moved Angela Merkel on Friday spoke of her "deep shame" at the "inconceivable" crimes of the Nazis during World War II.

"I bow my head before the victims of the Shoah (Holocaust)," she said.

At the entrance of the camp, the weakest, the youngest and the oldest were picked out and taken straight to the gas chambers, the remains on which Merkel also visited.

Black-and-white photos displayed at the site taken by SS officers in 1944 show groups of child prisoners arriving wearing hats and holding hands.

One of the children was Bogdan Bartnikowski, who was taken to Auschwitz with his mother at the age of 12 following the failed Warsaw Uprising on August 12, 1944.

Now 87, he remembered the first hours of his arrival.

"It was a great shock. I suddenly had to take my clothes off," he said, speaking in front of Merkel and Polish Prime Minister Mateusz Morawiecki. 

"It was the waiting room to hell," he said.

Later, thinking he was going to be released along with the other children, Bartnikowski was told by a guard: "Look at those chimneys. There is no other exit. That is the only way you're getting out of here."

As Soviet troops advanced, the remaining Nazi guards tried to destroy the gas chambers at Auschwitz.

The camp was eventually liberated on January 27, 1945.

The Red Army soldiers found 7,000 emaciated prisoners still being held there, including Italian writer Primo Levi whose haunting memoir "If This Is A Man" has become one of the totemic texts of the Holocaust.

'It was an absolute shock'

The camp is now a protected site visited by over two million people a year, including many school groups.

Pavel Chaloupecky, 40, a teacher of French and English in Prague, said he was visiting Auschwitz for the fourth time with a group of 35 teenagers.

"The first time I came, it was an absolute shock. Auschwitz represents the calculated and total suppression of humanity," he said.

"Since then, my experience has become more personal with each visit. I've noticed the steps worn down by Nazi boots and I tell myself that my shoes are treading on the same steps as those people," he said.

After each visit, he asks the children to express their emotions. He said seeing Auschwitz helps them understand that "nothing is taken for granted".

"When you ask the question about whether this could happen again, they say yes," he said.

Chaloupecky's late grandmother was a survivor of Auschwitz and, like many of those who made it out alive, she kept silent about what happened.

"My grandmother did not talk about it. She was afraid she would be faced with total incomprehension," he said.

Only the numbers tattooed on her arm told the story.

At a time when the few remaining survivors of Auschwitz are dying out, Merkel praised the "strength and courage" of those who do tell their stories.

She added: "Silence cannot be our only response. This place demands that we keep the memory alive".