Thousands of Christians have gathered in Jerusalem for an ancient fire ceremony that celebrates Jesus' resurrection.

In a ritual dating back at least 1,200 years, they crowded Saturday into the Church of the Holy Sepulchre, where Christian tradition holds that Jesus was crucified, buried and resurrected.

During the annual ceremony, top Eastern Orthodox clerics enter the Edicule, the small chamber marking the site of Jesus' tomb.

They then emerge to reveal candles said to be miraculously lit with "holy fire" as a message to the faithful from heaven. The details of the flame's source are a closely guarded secret.

Roman Catholics and Protestants marked Easter in March, in accordance with the Gregorian calendar. Eastern Orthodox churches celebrate Easter this week using the older Julian calendar.