Though it's not an official part of Hajj, many pilgrims also go to Medina, another holy city in Saudi Arabia.
The five-day pilgrimage represents one of the five pillars of Islam. Nearly 14,000 global and domestic flights have so far transported pilgrims with around 21,000 buses also used.
They will spend the night there in fire-resistant tents in the desert, where temperatures top 40 degrees Celsius (104 Fahrenheit).
They traditionally slaughter sheep for the three-day Eid al-Adha, a tribute to the prophet Abraham's sacrifice of a lamb after God spared Ishmael, his son.
While a holy, once-in-a-lifetime experience for pilgrims, the hajj is by no means an easy journey.
These movements done by the pilgrims nearly at the same time is so massive that special arrangements need to be made. "It is the best feeling of my life to be able to perform the hajj", said Mostafa, 50, as he looked at the cube-shaped structure towards which Muslims turn in prayer five times a day.
After prayers in Mecca, pilgrims will head to an area called Mount Arafat on Monday, where the Prophet Muhammad delivered his final sermon.
Pilgrimage is also the backbone of a plan to expand tourism under a drive to diversify the kingdom's economy away from oil.
Paul Pogba criticizes Manchester United attitude
When asked about a disastrous first-half display, Pogba refused to state whether manager Jose Mourinho was at fault. We should be mad. "They had more hunger than us and the result is the right one for them".
Saudi Gazette Makkah bureau chief on Monday boarded a S92 aircraft of the security aviation, which flew at 2,000 feet above sea level, and monitored the stand of over two million pilgrims in Arafat.
The 2018 pilgrimage comes amid a widening crackdown on political dissent in Saudi Arabia, an absolute monarchy aggressively pursuing a campaign to clean up its image as one of the world's most restrictive countries.
Bassam said they would continue their air surveillance of the movement of the pilgrims until the 13th of Dhul Hijja (Aug. 24).
By Thursday, more than 1.6 million people had arrived in Saudi Arabia for the pilgrimage, AFP reported.
They have cut all ties with Qatar and banned all flights to and from Doha.
Nayef Ahmed, 37, told Reuters that he sold a plot of land in Yemen, which is embroiled in a three-year proxy war between Saudi Arabia and Iran, to afford the trip.
Saudi Arabia, and the three other Arab countries, closed land, air and sea links with Qatar in June past year, accusing it of funding terrorism, something Doha denies.
Haj season is being managed with tight security to ensure the well being of pilgrims.