Thousands of people began moving today from the holy city of Mecca to nearby Medina for the start of the hajj, the annual Islamic pilgrimage.

The video above shows huge crowds moving inside of the Ka’bah Mosque in Mecca and walking around the Kabba, a masonry cube at the sacred mosque, before leaving the shrine to Medina.

Nearly three million people are expected in this year’s hajj. The pilgrimage is considered a mandatory religious duty for Muslims, who must complete it at least once in their lifetime.

The pilgrimage to the holy city of Medina also started amid tight security.

The Saudi authorities deployed 100,000 security personnel, including members of the counter-terrorism and the emergency civil defence units, and 5,000 CCTV cameras.

The measure follows earlier attacks claimed to be perpetrated by Isis-affiliated groups, in which more than 60 people were killed.

Earlier this month, more than 100 people died after a construction crane toppled into the courtyard of Mecca’s Grand Mosque.