The highest temperatures at the holy sites were predicted by the Met Department to range from 45 to 48 degrees Celsius in the afternoons.
According to Saudi national meteorological center chairman Ayman Ghulam, “the expected climate for hajj this year will witness an increase in average temperatures of one and a half to two degrees above normal in Makkah and Medina.”
One of the five pillars of Islam is the hajj, which starts on June 14 and must be completed at least once by all Muslims who have the means to do so.
It consists of a four-day sequence of rituals performed in Mecca and the surrounding areas in oil-rich Saudi Arabia.
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Last year more than 1.8 million Muslims took part in the hajj, official figures showed.
More than 2,000 people suffered heat stress, according to Saudi authorities, after temperatures soared to 48 degrees Celsius (118 degrees Fahrenheit).