Thursday is also Eid Al-Adha. It has traditionally been the most dangerous day of Haj because vast numbers of pilgrims attempt to perform rituals at the same time in a single location.

Street 204 is one of the two main arteries leading through the camp at Mina to Jamarat, where pilgrims ritually stone the devil by hurling pebbles at three large pillars.

Photographs published on the civil defence Twitter feed showed pilgrims lying on stretchers while emergency workers in high-visibility jackets lifted them into an ambulance.

"Work is under way to separate large groups of people and direct pilgrims to alternative routes," the Saudi Civil Defence said on its Twitter account.

The pilgrimage, one of the world's largest annual gathering of people, has been the scene of deadly stampedes in the past, as well as other disasters including tent fires and riots.

However, massive infrastructure upgrades and extensive spending on crowd control technology over the past two decades had made such events far less common.  -Reuters