Mourning processions, meetings and fasting marked "Yaum - e - Ashura" in Telangana and Andhra Pradesh on Wednesday.
The day was observed in memory of the martyrdom of Imam Hussain, a grandson of Prophet Mohammed, and others in the battle of Karbala.
"Bibi ka alam", the traditional mourning procession by Shias, was underway in the old city of Hyderabad.
The Sunni Muslims observed the day by fasting and holding meetings to remember the sacrifices of Imam Hussain and his followers who were martyred in 61 Hijri or 680 CE at Karbala, in present day Iraq.
Poor feeding and distribution of water and juice also marked the 10th day of Muharram, the first holy month of Islamic calendar.
The fasting is observed on two days - ninth and 10th or 10th and 11th Muharram.
Muharram rituals are all aimed at remembering the great sacrifices of Imam Hussain and his followers who refused to bow to despotic and tyrannical authority.
Blood oozed out from the heads and chests of hundreds of bare - chested Shia mourners participating in the "Bibi ka alam" march and flagellating themselves with sharp - edged objects.
Amid cries of "Ya Hussain" and recitation of Marsiyas (elegies) and noha - khwani (poems expressing sorrow), the barefoot youths, using knives, blade - encrusted chains and other sharp - edged weapons, inflicted injuries on themselves to show solidarity with the sufferings of the martyrs.
Others were seen weeping and beating their chests.
The massive procession began from "Bibi Ka alawa", with the "alam" insignia of the martyrs kept on 'Rajni', an elephant brought from Nehru Zoological Park.
The "Bibi ka alam" is believed to contain a piece of wooden plank on which Bibi Fatima Zehra, daughter of Prophet Mohammed, was given the final ablution.
The "alam" was installed over 430 years ago during the Qutub Shahi period.
It also contains six diamonds and other jewellery donated by Mir Osman Ali Khan, the seventh and last Nizam.
The procession passed through various parts of the old city including historic Charminar, with thousands of people, irrespective of religion and caste, standing along the roads to pay their respects.
Prominent personalities including politicians, police, civil officials and family members of Nizam, the ruler of erstwhile Hyderabad state, will make offerings to the 'alam' at different places.
After covering a distance of seven km, the procession will culminate after the sunset at Chaderghat on the banks of Musi river.
Water and 'sharbat' were distributed from stalls set up at various places in the old city.
Elaborate security arrangements were in place for peaceful and smooth conduct of the procession.
Closed - circuit television cameras were also installed on the procession route to keep a tight vigil.
Police also imposed restrictions on traffic movement at various points in the old city.
Hyderabad has the second largest population of Shias in India after Lucknow.
Muharram was also observed in various parts of Telangana and neighbouring Andhra Pardesh in the traditional manner.
In several towns and villages of Telangana, people irrespective of their religion and caste observed Muharram in their unique, distinct style and in accordance with the local traditions.