The stampede that killed more than 700 people during the pilgrimage in Saudi Arabia was triggered when two large crowds of pilgrims collided as they came into an intersection from different directions, officials and witnesses said.

An Egyptian man who witnessed Thursday�s disaster said Friday that train delays and heavy traffic on the roads left more pilgrims walking to reach key sites on the pilgrimage route.

He said crowds were moving Thursday morning from Mount Arafat, where pilgrims stand to pray in the most important ritual of the pilgrimage, to Mina�a tent encampment on the outskirts of the holy city of Mecca. The vast tent city at Mina houses some two million people attending the pilgrimage, or hajj, this year.

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This article was written by Ahmed Al Omran & Asa Fitch for The Wall Street Journal on Sep. 25, 2015. Ahmed Al Omran covers Saudi Arabia and the Middle East for The Wall Street Journal. Asa Fitch writes about economics, finance and investment from The Wall Street Journal's Dubai bureau. His coverage areas include the economies of the Gulf and the region's large sovereign wealth funds.