Orthodox Christians believe Jesus was crucified and buried at the site where the Church of the Holy Sepulcher now stands, and that a flame appears spontaneously from his tomb on the day before Easter to show he has not forgotten his followers.
Worshippers carrying torches or bundles of 33 tapers signifying the years of Jesus' life waited in excited anticipation as the Greek Orthodox Patriarch in the Holy Land, Theofilos III, removed his embossed gold-and-white mitre and descended with Greek Orthodox, Armenian and other Eastern rite clergy into the tomb.
After the flame appeared there, he passed it from inside the tomb to believers inside the church's main hall, who rushed to light their own candles and torches, illuminating the darkened church within seconds and filling it with smoke. Church bells pealed, and some of the faithful passed their hands through the flames they held, reflecting their belief in the fire's divine and beneficial nature.
Worshippers hoisted one of the clerics who had gone into the tomb on their shoulders after he emerged, waving a bundle of lit tapers.
"It's (a) very huge experience and it's a holy place," said a Serbian woman who identified herself only as Irena.
Light from the holy fire was taken afterward to the Church of the Nativity in the West Bank town of Bethlehem, where tradition holds Jesus was born, and aboard special flights to Athens and other cities, linking many of the 200 million Orthodox worldwide to their spiritual core.
The thousands who filled Jerusalem's cavernous Church of the Holy Sepulcher began lining up for the ceremony hours earlier. Video screens set up in various places in the Old City broadcast the ceremony live for the thousands more who could not fit inside.
Some of the celebrants held church flags, while others beat hand drums and sang hymns.
The various Orthodox denominations grouped into different areas of the church, which was heavily secured by Israeli forces.
Police spokesman Shmuel Ben-Ruby said about 2,500 police were stationed in the area, including as many as 1,500 within the church itself. He estimated that between 8,000 and 10,000 worshippers packed the church and about 7,000 more spilled over into its cobbled courtyard.
The holy fire ritual dates back at least 1,200 years. The precise details of the flame's source are a closely guarded secret.
This year, Orthodox Easter coincides with observances by other Christian denominations, bringing a large number of Easter pilgrims to the narrow alleys of Jerusalem's Old City.