During the annual Hajj pilgrimage in Saudi Arabia, one of the most important events on the Muslim calendar, at least 450 people died under a scorching sun as they prayed at sacred sites around the holy city of Mecca.

Amid maximum temperatures that ranged between 108 Fahrenheit and 120, according to preliminary data, and throngs of people, many passed out and needed medical care. The pilgrims, some who have saved their whole lives for the Hajj, spend days walking and sleeping in tents during their journey to Mecca, the holiest city for Muslims. The Hajj is one of Islam’s five pillars, and all Muslims who are physically and financially able are obliged to embark on the pilgrimage.

Indonesia has so far reported the most deaths, 199, and India reported 98. The countries said at this point that they could not be sure that heat was the cause of all the deaths, though relatives of the missing and dead and tour operators have said the heat was at least a contributing factor.

The number of dead is expected to rise as neither Saudi Arabia nor Egypt, where many pilgrims come from, has released death tolls for their citizens.

Egypt is alarmed enough that it has set up crisis centers to receive distress calls and coordinate the government’s response as families brace for a high death toll as many people have been reported missing.

This year, more than 1.8 million Muslims traveled to Mecca, 1.6 million of them from outside Saudi Arabia, according to the Saudi General Authority for Statistics.

Many complained that there were not enough cooling stations or water for all the pilgrims, and there were early reports that part of the problem was that many people did not officially register for the pilgrimage, possibly to avoid the steep costs of Hajj package tours.

Many of the pilgrims are older people who have spent years saving up to travel to the holy city. In the days before and during the holy period of Eid al-Adha, pilgrims visit several holy sites, including circling the Kaaba, and praying on Mount Arafat.

On a Hajj Facebook group with more than 900,000 members, Egyptians posted appeals for their missing relatives. In one, a woman left a message for her mother: “Mom, It’s me Rabab. I’ll wait for you outside King Khaled’s Bridge … Please see this post. I am dying for you. You’re the light of my eyes.”

Other countries reporting death tolls include Jordan, Tunisia and Pakistan.

Jordan’s foreign ministry said 75 pilgrims had died “as a result of the intense heat wave.”

Tunisia’s minister of Religious Affairs, Ibrahim Chaibi, said 49 Tunisians had died. He said that number was expected to rise as the number of pilgrims traveling on tourist visas became more clear, according to Tunisia’s state-run news agency.

One Egyptian tour operator said that because of increasing fees for Hajj package tours, as well as the devaluation of the Egyptian pound, many pilgrims opted for tourist visas, which had burdened the facilities set up in Mecca and the surrounding holy sites.

The man, who spoke from Mecca, described severe conditions for unregistered pilgrims. Speaking on the condition of anonymity because of security concerns, he said unregistered pilgrims had no tents and were exposed to extreme heat. He said there were too few buses, so many pilgrims walked distances of more than 12 miles.

Hind Hassan, from Egypt, said her aunt Safa Tawab died during the Hajj and that the tour company that arranged her trip hid the news until the family found her name on a list of the deceased published online.

A friend who had accompanied Tawab, 55, told the family that the pilgrimage was like “walking in the road of death because of the heat and the lack of water,” Hassan said.

Mahmoud Qassem, a member of Egypt’s Parliament, blamed dubious tour operators for “the exposure of Egyptian pilgrims to deception and fraud by tourism companies,” calling for a police investigation.

The Hajj has been the site of several tragedies, including a stampede in 2015 that killed more than 2,200 people. In recent years, with rising temperature, many pilgrims have also succumbed to heat stress.

Islamic Relief, a global aid agency based in London, has warned about the impact of climate change on the Hajj since 2019.

“Should the world’s emissions continue in a business-as-usual scenario, temperatures in Mecca will rise to levels that the human body cannot cope with,” Shahin Ashraf, the organization’s head of global advocacy, said in an emailed statement Friday.

In Pakistan, which has lost at least 35 people, according to official figures, mourners gathered to honor their dead. Dozens of people in Chaman, a city in Balochistan province along Pakistan’s border with Afghanistan, offered condolences outside the house of Abdul Bari Kakar. The 49-year-old Kakar ran a gas cylinder shop and had saved up for months to make what was his third trip, his relatives said.

He chose to go “to pray for his grandfather who passed away years ago,” said Sardar Wali, his son.

“We are saddened by his death,” he said, “but he was fortunate to have died in the Holy Land.”

This article originally appeared in The New York Times.