More than two million Muslims begin on Friday the annual hajj, which is one of the five pillars of Islam and must be undertaken by all Muslims with the means at least once in their lives.
The hajj, one of the world's largest annual religious gatherings, consists of a series of religious rites which are completed over five days in Islam's holiest city and its surroundings in western Saudi Arabia.
"All of the arms of state have been deployed (and) we are proud to serve as 'God's hosts'," said security forces spokesman Bassam Attia.
In total, some 2.5 million faithful, the majority from abroad, will undertake the pilgrimage this year.
"More than 1.8 million visas were delivered online without the need for middlemen. It's a success," said hajj ministry official Hatim bin Hassan Qadi.
"We feel cleansed by achieving this pillar of Islam and meeting people from across the world. It's marvelous," said Mohamed Jaafar, a 40-year-old Egyptian pilgrim.
"It's an indescribable feeling. You have to live it to understand it," said an Algerian in his fifties completing the pilgrimage for the first time.
"It's a golden opportunity and moment," said his female companion.
Built in a desert valley, Makkah is home to the Kaaba, a cube structure that is the focal point of Islam and draped in a gold-embroidered black cloth.
Muslims around the world pray towards the Kaaba, which is located in the Grand Mosque, and pilgrims walk around it seven times.
Worshippers participated in weekly prayers late on Friday morning.
"The whole world is here... being here in Mecca is the best feeling," said Mohamed Barry, a pilgrim from Britain.
During the pilgrimage, separate streams of men and women, grouped by nationality, will travel to Mina on foot or in buses provided by the authorities.
A district of Mecca, Mina sits in a narrow valley surrounded by rocky mountains and is transformed each year into a vast encampment for pilgrims.
A total of "350,000 air-conditioned tents have been pitched," a Saudi official said.
Worshippers will climb Mount Arafat, also known as the "Mount of Mercy", for hours of prayers and Koran recitals.
After descending, they will gather pebbles and perform the symbolic "stoning of the devil".
That marks the beginning of Eid al-Adha, the festival of sacrifice, marked on Sunday.
Pilgrims then return to the Grand Mosque to perform a final "tawaf" or walk around the Kaaba.