At least 107 Muslim pilgrims were trampled to death Thursday when panic erupted after several fell off an overpass, the official Saudi news agency reported.

The stampede occurred at midday as pilgrims performed a ritual known as "stoning the devil" on the last day of the hajj, an annual pilgrimage to Mecca which this year drew an estimated 2.3 million Muslims.

The stampede occurred on the plains of Mina outside Mecca. Some elderly and sick pilgrims fell off an overpass, the Saudi Press Agency said. In the rush that ensued, scores were trampled, it said.The agency said the casualty figure was preliminary. Security officials did not have a breakdown of nationalities. Islam requires all Muslims who can afford it to make the pilgrimage to Mecca, Islam's holiest site, at least once in their lives.

Today, crowds of tens of thousands had struggled with heat that hovered above 100. Helicopter crews hovered overhead to spot pilgrims fainting, and workers threw bags of chilled water from trucks to those making their way to the pillars.

To shield themselves, pilgrims covered their heads with towels or carried umbrellas, some inscribed with "God is great."

Police using loudspeakers had pleaded in Arabic, English, French and Urdu for pilgrims to move along quickly. Other police with batons made room for pilgrims wanting to escape the crowds.

The stampede was only the latest tragedy to befall the hajj, which in the past has been marred other stampedes, fires and political protests that turned violent. Until today, Saudi officials had praised the smooth running of this year's pilgrimage.

At the ceremony at the pillars, pilgrims from more than 100 countries throw seven chickpea-size stones at each of the pillars on the Mina plain three times over as many days.

Today marked the final day of the four-day hajj, which closes with pilgrims circling the Kaaba.

The Kaaba, a cubelike structure at the Grand Mosque in Mecca, is considered the spiritual center of Islam.