Paramedics and police officers offered relief by spraying them with water or fanning their faces with folded cardboard.
In the white-tented city of Mina, some even sought shelter from the sun by lying under parked trucks.
Shaaban al-Sisi, a 67-year-old Egyptian pilgrim, said the heat was not enough, he also had to struggle with a chronic heart condition.
"The hot temperatures are exhausting for me. But I won't leave...until I perform all the rituals," he said.
Saudi authorities have dispatched more than 32,000 health workers to help fend off heatstroke, dehydration and exhaustion, especially among the elderly.
More than 1.8 million worshippers are taking part in this year's hajj, a dramatic increase on the 926,000 from last year, when numbers were capped at one million.
Only 10,000 were allowed in 2020, at the height of the coronavirus pandemic, rising to nearly 59,000 a year later.
Many Muslims prefer to embark on the pilgrimage at a younger age, knowing the physical challenges.
But modest finances force others to wait until they can afford it -- a process that could last well after retirement.
Sitting under a green umbrella, Fadia Abdullah said she felt "the joy of the whole world" after finally making it to hajj.
"I am living a moment that I have waited a lifetime for," the 67-year-old Egyptian woman said.
Rahim, an Indonesian pilgrim who only goes by his first name, complained of "extreme crowding".
But he said he was still grateful for the chance to embark on hajj for his fifth and probably final time.
"My dream of hajj has come true again before I die," said the 76-year-old.
