KARBALA: More than 600 pilgrims in Iraq were briefly hospitalized with respiratory problems after inhaling chlorine as the result of a leak at a water treatment station, authorities said Sunday.

The incident took place overnight on the route between the two Shiite holy cities of Najaf and Karbala, located in the center and south of Iraq respectively.

This year, several million Shiite Muslim pilgrims are expected to make their way to Karbala, which houses the shrines of the revered Imam Hussein and his brother Abbas.

There, they will mark the Arbaeen — the 40-day period of mourning during which Shiites commemorate the death of Hussein, grandson of the Prophet Muhammad.

In a brief statement, Iraq’s health ministry said “621 cases of asphyxia have been recorded following a chlorine gas leak in Karbala.”