Ali al-Mayalee, deputy governor of Karbala, put the total number of pilgrims at six million on Tuesday.
He said thanks to adopted security measures, no incident was reported during the mourning processions.
More than 30,000 individuals were tasked with providing the security of the event.
Also, the number of pilgrims in Kadhimiya on the same day is estimated to be above two million.
This is according to Sa’d al-Hajieh, deputy secretary of the Astan (custodianship) of Al-Kadhimiya holy shrines. He also noted that the mourning processions were held in a fully secure environment.
According to Iraqi media, more than 17,000 foreign pilgrims had arrived in the Arab country prior to the start of the processions.
Ashura is the tenth day of Muharram, the first month in the lunar Hijri calendar.
Shia Muslims, and others in different parts of the world, hold ceremonies every year in Muharram to mourn the martyrdom anniversary of Imam Hussein (AS) and his companions.
The third Shia Imam (AS) and a small group of his followers and family members were martyred by the tyrant of his time - Yazid Bin Muawiya, in the battle of Karbala on Ashura in the year 680 AD.