The central government rushed 800 anti-riot policemen to violence-hit Uttar Pradesh and Madhya Pradesh.
A Home Ministry official in Delhi said two companies of Rapid Action Force (RAF) were sent to Meerut and one company each to Agra and Hapur in Uttar Pradesh.
Clashes turned deadly in Madhya Pradesh where six persons were killed and dozens injured, forcing officials to impose curfew in Morena, Gwalior and Bhind districts. Protests were also held Bhopal as agitators blocked roads in the state capital.
Madhya Pradesh Chief Minister Shivraj Singh Chouhan made a passionate appeal for peace.
Police said two were killed in Bhind and one in Morena while three died in Gwalior. The dead in Morena was identified as Rahul Pathak, a student leader.
Gwalior District Magistrate Rahul Jain told IANS that at least 65 persons have been injured in violence, including policemen, and the condition of a few injured is said to be serious.
"Three people have been conformed dead in Gwalior," he said.
A man identified as Pawan Kumar was killed in Rajasthan's Alwar as violence was also reported from other parts of the state including Jaipur, Ajmer. Jaisalmer, Barmer, Jodhpur and Udaipur.
Punjab and Haryana also saw widespread protests.
Shops, educational institutions and other establishments remained closed and Class 10 and 12 examinations were deferred in Punjab, which has the highest concentration of Scheduled Castes, constituting nearly 32 per cent its 2.8 crore population.
Hundreds of protesters carrying swords, sticks, baseball bats and flags forced shopkeepers and other establishments in Jalandhar, Amritsar and Bathinda too shut down.
Protests also took place in Rohtak and other towns of neighbouring Haryana.
In Bihar, activists disrupted rail and road traffic. Mobs shut down markets and shops as well as educational institutions, police said.
Supporters of the Bhim Army and other Dalit outfits halted over three dozen long-distance and local trains, stranding thousands of passengers.
Violence was reported from Vaishali, Muzaffarpur, Nawada, Patna and Bhagalpur when protestors clashed with police.
One person was killed and over 100 were injured as violence also erupted in parts of Uttar Pradesh as protesters attacked shops, looted some and pelted stones at police in Hapur, Agra, Meerut, Saharanpur and Prime Minister Narendra Modi's Lok Sabha constituency Varanasi.
Maximum violence in the state was reported from western Uttar Pradesh, where the protesters took to the streets and went on rampage. Two persons were critically injured in police firing in Muzaffaranagar, one of whom later succumbed.
More than 450 people, including a former Bahujan Samaj Party (BSP) legislator, have been arrested.
Many cars were targeted and their window panes smashed. At some places, government property was targeted.
Some people reportedly fired at a police team in Meerut while a passenger bus was set on fire.
Also in Meerut, over 500 Dalit youths targeted the media and broke their cameras as they were trying to photograph the protests.
Gujarat's major towns and cities also saw protests by Dalits amid reports of vandalism from Ahmedabad and Jamnagar.
Amid widespread anger and violence, the Modi government filed a review petition in the Supreme Court to seek recall of its judgment that ruled that there would be no automatic arrest of an accused following a complaint moved under the Scheduled Castes and Scheduled Tribes (Prevention of Atrocities) Act, 1989.
The Supreme Court had held on March 20 that police will hold an inquiry to ascertain the veracity of the complaint filed under the act before acting on it.
Union Law Minister Ravi Shankar Prasad said the government "with due respect, does not agree with the reasoning given by the apex court".
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)