As the sirens began at 10 a.m. local time (0800 GMT), traffic came to a total standstill as drivers stood next to their cars and pedestrians stopped walking, many of them standing to attention or with their heads bowed.

Holocaust Memorial Day began Wednesday night with a ceremony at Jerusalem's Yad Vashem Holocaust Memorial Institute, attended by state leaders, foreign diplomats, and Holocaust survivors and their relatives.

Six survivors lit six beacons honoring the 6 million Jews killed by the Nazis and their collaborators.

"Sixty-three years have passed since the Satanic factories of death of the Nazis and their collaborators ceased to operate, yet with the passing of time, the dimensions of the Holocaust still remain beyond comprehension, unfathomably shocking, unacceptably chilling," Prime Minister Ehud Olmert said at the ceremony.

"Who would have believed that 63 years later, hatred of Jews and Israelis would rear its ugly head in so many different places around the globe, provocatively and venomously, inciting hatred?" he asked. "The voices of those who deny the Holocaust are also being heard. To them, the haters, the deniers, and all the conspirators of evil and to all of those who allow them to function within their realms, we say today: This shall never happen again."

In a second thinly veiled comparison of Nazi Germany to contemporary Iran, Israeli President Shimon Peres told the hundreds of Holocaust survivors and other Israelis at a Yad Vashem ceremony on Wednesday that the world could have faced destruction if Nazi dictator Adolf Hitler had succeeded in acquiring nuclear weapons.

Commemorations continue Thursday with ceremonies at Yad Vashem and television and radio channels broadcasting special programs focusing on the Nazi attempt to murder the Jews of Europe.

The names of the victims will be read out at the Knesset and at Yad Vashem's Hall of Remembrance.

The United Nations has designated Jan. 27, the day the Auschwitz death camp was liberated in 1945, as international Holocaust Remembrance Day, but Israel has traditionally marked it on the 27th day of the Jewish month of Nissan, one week before Independence Day, to symbolize the birth of the Jewish state from the ashes of the Holocaust.

According to counts held before and after the war, two-thirds of Europe's 9 million Jews perished at the hands of the Nazis and their collaborators.