Christians believe Jesus was crucified, buried and resurrected at the site where the Church of the Holy Sepulcher now stands in the Old City of Jerusalem. While the source of the holy fire is a closely guarded secret, believers say the flame appears spontaneously from his tomb on the day before Easter to show Jesus has not forgotten his followers.
The ritual dates back at least 1,200 years.
Thousands of Christians waited outside the church for it to open Saturday morning. Custody of the Church of the Holy Sepulcher is shared by a number of denominations that jealously guard their responsibilities under a fragile network of agreements hammered out over the last millennia. In accordance with tradition, the church's doors were unlocked by a member of a Muslim family, who for centuries has been the keeper of the ancient key that is passed on within the family from generation to generation.
Once inside, clergymen from the various Orthodox denominations in robes and hoods jostled for space with local worshippers and pilgrims from around the world.
Top Orthodox clergymen descended into the small chamber marking the site of Jesus' tomb as worshippers eagerly waited in the dim church clutching bundles of unlit candles and torches.
After a while, candles emerged lit with "holy fire" — said to have been lit by a miracle as a message to the faithful from heaven.
Bells rang as worshippers rushed to use the flames to ignite their own candles.
In mere seconds, the bursts of light spread throughout the cavernous church as flames jumped from one candle to another. Clouds of smoke wafted through the crammed hall as flashes from cameras and mobile phones documented what is for many, the spiritual event of a lifetime.
Some held light from the "holy fire" to their faces to bask in the glow while others dripped wax on their bodies.Israeli police spokeswoman Luba Samri said tens of thousands of worshippers participated in the ceremony.
Many couldn't fit inside the church and the narrow winding streets of the Old City were lined with pilgrims.
The "holy fire" was passed among worshippers outside the Church and then taken to the Church of the Nativity in the West Bank town of Bethlehem, where tradition holds Jesus was born, and from there to other Christian communities in Israel and the West Bank.
Later it is taken aboard special flights to Athens and other cities, linking many of the 200 million Orthodox worldwide.