At least 19 pilgrims are said to have died from extreme heat in the ongoing Hajj pilgrimage in Saudi Arabia, according to officials.

Jordan’s foreign ministry reportedly said 14 of its nationals succumbed t0 sun stroke resulting from the extreme heat wave with 17 others reported missing.

Meanwhile, the Iranian Red Crescent confirmed that five Iranian pilgrims also died, but did not state how they died.

According Jordanian officials, searches were ongoing for those missing.

Hajj is one of the largest mass gatherings in the world. More than 1.8 million pilgrims were said to be taking part this year.

The pilgrimage will end on Wednesday. Saudi officials say as part of heat mitigation measures, they have set up many climate-controlled areas. They distribute water and offer advice to pilgrims on how to protect themselves from the sun.

The Saudi health ministry also issued an advisory, asking pilgrims to stay hydrated and avoid being outdoors during the hottest hours of the day between 10:00 and 16:00.

Last year, at least 240 people died. And in the worst Hajj disaster, a deadly crush in 2015 killed more than 2,000 people.