Flooding from the unusually heavy downpours hit hardest in the Red Sea coastal city of Jiddah, about 40 miles (60 kilometers) away from the holy city of Mecca and its surrounding sacred sites where the 3 million Muslims from around the world were performing the rites of the pilgrimage.

Most of the deaths occured in Jiddah, where streets were swamped with water, some houses collapsed and mudslides took place, and in areas around the main highway to Mecca, Civil Defense officials said.

It did not immediately appear that any pilgrims were among the dead. Jiddah’s civil defense chief Capt. Abdullah al-Amri said 21 of the victims were identified as Saudis and the rest were believed to be residents of Saudi Arabia.

Wednesday’s downpours snarled the opening day of the hajj, drenching pilgrims and knocking out roads that caused epic traffic jams as the faithful tried to make their way to the holy sites. The rains, if they continue as meteorologists predict, could raise safety hazards — particularly the perennial danger of deadly stampedes, since a trip-up on slippery walkways could lead to people getting trampled in crowds.

The Unicef statement said more than 50 schools had also been closed since fighting in neighbouring Yemen spilled across the border last week.

Encouraging pilgrims to get vaccinated at least two weeks before departure is the best way to stop its spread, said U.S. and Arab experts, including Saudi Arabia’s deputy minister for preventative medicine.