Hannah Lewis fought back tears as she recounted seeing her mother killed by the Nazis in 1943.
Before an audience including Boris Johnson and other MPs, Mrs Lewis told her story to the annual HMD ceremony at City Hall.
She was six when her family was moved to a work camp in Adampol, a Polish village a few miles from her hometown of Wlodawa.
Her father escaped from the camp and joined the Partisans but “my mother and I stayed in Adampol. “One day there was this great whack on the door and my mother with great dignity got on her knees and gave me a huge hug and kisses and walked quietly to the door.
“She opened it and closed it firmly behind her. When she didn’t come back, I got up and opened the door.
“There she was with others being marshalled towards the well. She didn’t look at me and as I tried to catch her eye suddenly an order was given and they [the Nazis] started to shoot.
“I saw her fall. I saw the blood on the ground. If I screamed it was internal.”
Mrs Lewis was liberated in 1945 by a Russian soldier who picked her out of a trench and she was reunited with her father.
Mr Johnson gave a reading from survivor Elie Wiesel’s 1986 Nobel Peace Prize acceptance speech. He added that “today we remember the millions of people who lost their lives in both the Holocaust and other appalling acts of genocide.
“Recent events here in London and in our sister city, Paris, as well as other parts of the world, remind us of the importance of cherishing and defending freedom and tolerance.”
Other speakers included Rabbi Raphy Garson of Elstree’s Ohr Yisrael congregation, who observed that “as we remember the millions of victims of the Shoah and other genocides, we must reflect upon the fact that mass murder is not a matter of abstract statistics. For every person dreams and aspirations were destroyed. “This abiding imperative teaches that we are the guarantors of each other’s destiny.”