One of the rituals is known as the "Tuwairij run", which sees pilgrims run down streets leading to the Imam Hussein Mosque in commemoration of the run from the ancient village of Tuwairij to Karbala that was undertaken during the 7th Century battle by the cousins of Hussein's half-brother Abbas.
Tens of thousands of Shiite Muslims converge on the holy city for the occasion, which marks the anniversary of the death of Imam Hussein, one of the grandsons of the prophet Mohammed.
The incident occurred when a walkway collapsed, causing panic and a stampede.More news: Team USA Stifles Giannis Antetokounmpo, Beats Greece
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The death toll released by the Iraqi Health Ministry was expected to rise, with at least 10 people in critical condition.
Earlier, processions of black-clad worshippers made their way to Hussein's gold-domed shrine in Karbala, carrying black flags with "Hussein" written in red and wailing loudly. Hussein's killing has been attributed with cementing the schism between Shiite and Sunni Islam. Another official told the AP that there had been no collapse or crack in the walkway near the shrine.
Iraqi Shi'ite Muslims take part in a mourning procession on the tenth day of the lunar month of Muharram which marks the day of Ashoura on Tuesday, September 10. In 2004, at the height of Iraq's sectarian violence, 143 people were killed in near simultaneous suicide and other bombings at shrines in Baghdad and Karbala during the Ashoura procession. However, this is reportedly the deadliest such stampede in recent history. Numerous worshippers beat their chests and lash themselves with chains in an expression of grief and regret for not being able to help the murdered grandson of the Prophet.