Saudi Arabia has barred more than 269,000 people without permits for the annual Hajj pilgrimage from entering Mecca this week, authorities said, as the world's largest annual gathering of people has officially begun.

Millions of Muslims from all over the world have converged on Mecca in Saudi Arabia to partake in Islam's annual Hajj pilgrimage.

Here is a look at the hajj, one of the largest mass gatherings in the world, which starts in Saudi Arabia on Wednesday.