By Adam Easton
BBC News, Warsaw
Commemorations to mark the Holocaust Memorial Day have begun in Poland.
Auschwitz has become the most powerful symbol of the Holocaust
The UN last year passed a landmark resolution to make 27 January an annual day of remembrance for six million Jews killed during World War II.
The date marks the anniversary of the liberation of the Nazi death camp in Auschwitz, southern Poland.
As a mark of respect, the Archbishop of Krakow, Stanislaw Dziwisz, has called on Poles to light candles in their windows in remembrance.
During the war, Poland's three million-strong Jewish community was almost completely wiped out.
Survivors, government and religious leader will gather in Auschwitz later on Friday.
On Thursday, Holocaust survivors mixed with the young at the memorial to the victims of the Warsaw Ghetto.
The tram has the Star of David instead of a number
A 1940s tram marked with the Star of David - like the ones that used to travel through the ghetto - will be seen again on the streets of Warsaw on Friday.
It will be empty. Nobody will get on or off.
Before World War II, Warsaw was home to the largest Jewish community in the world outside New York.