Shaking with emotion, a 91-year-old great-grandmother recalled her time in Auschwitz to an audience of London civic leaders on Monday.
Freda Wineman - whose parents and brother died in the camp - said that "in no time we were completely dehumanised. It was just hell.
"The smoke and smell of the crematoria made us terribly depressed as we knew what was happening and we were helpless and lost. It was very hard to keep going.
"Every two weeks or so there was another selection. They were the most terrifying moments.
"The losses I suffered and the experiences I endured are with me literally every day and every night. Our testimonies mean we will never be silenced."
At the City Hall event, Boris Johnson pledged that London would remain a "safe haven" for Jews.
"In the wake of the horrific attacks in Paris, and as we face an increased threat to our security, it is more important than ever that we stand strong in our beliefs of tolerance and freedom of speech," he said.
He was proud that the capital had "long been a safe refuge for all those who are persecuted, with many thousands of Holocaust survivors making it their home. London will continue to provide this safe haven."
Chief Rabbi Ephraim Mirvis warned that "the hatred and evil that inspired the Holocaust still exists today, which makes it all the more important to keep the memory of the Holocaust alive.
"If you reduce a person to a mere number, they are as of heads of cattle and you can commit the most horrific crimes on your fellow human beings.
"In Jewish tradition, we never count people. I believe that we owe it to the victims that we strengthen the connections we have with others. We must recognise the divinity within all people."
The 200-plus guests were also addressed by graduates of the Holocaust Educational Trust's Lessons from Auschwitz programme for students.
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