War veterans and civic leaders gathered in Geraldine Mary Harmsworth Park on Tuesday for a ceremony at Southwark's Holocaust memorial tree.
Rabbi Alan Greenbat from the Chief Rabbi's office conducted a short act of remembrance and prayers were led by the Anglican Bishop of Woolwich Rt Revd Christopher Chessun next to the tree planted in 2002 as a memorial to those who died in the Holocaust.
"Every day people stereotype, exclude and persecute because of race, religion, disability or sexuality," said Cllr Mann.
"Such hatred is a corrosive force, able to ruin lives and destroy communities and nations. It is present in small ways in daily life but is at its most lethal in prejudice, discrimination and racism.
"Acts of hatred involve making a choice. We choose to act or stand by and do nothing – or we choose to resist, to respect and to protect."
Cllr Mann has made "unity in diversity" one of the key themes of her mayoral year.
"Eleven days ago two parents of a 14-year-old were in the Old Bailey to hear a sentence passed on the teenager who had – in an unprovoked way – stabbed their son who three weeks later died.
"The lad who did the stabbing came after this local 14-year-old because he came from another school.
"There was antagonism and there was hatred simply because of the school someone was at."
Mr Hughes went on to call on world leaders to take advantage of the "new start in global politics" afforded by the election of Barack Obama to ensure "that all of our governments and all of our governments and all of our leaders – locally and nationally – never abuse their power and treat everybody as people of equal value whoever they are".
Wreaths were laid by representatives of Southwark organisations and embassies of countries from the former Soviet Union before two minutes' silence was kept.
A Holocaust Memorial Day ceremony was also held at City Hall with testimony from Rudi Oppenheimer, a survivor of the Bergen-Belsen camp. He was taken to the camp at the age of 12 and was put on the last train out of the camp in April 1945 before being liberated by the Russian army. The ceremony is available to watch online.