Protesters pelted stones, torched vehicles and faced tear-gas shells in the state capital and some other parts of Uttar Pradesh as police struggled to contain the fallout of the amended citizenship law.
The scattered incidents of violence were reported from Lucknow's old city and parts of Sambhal and Mau districts.
Internet services remained suspended for at least part of the day at various places, including Aligarh, Sambhal, Mau and Azamgarh districts.
Section 144 of the CrPc, which bans the assembly of people, had already been in force in the entire state for several days now.
Talking tough on TV, Uttar Pradesh Chief Minister Yogi Adityanath said the state government will make those who damaged property pay for it. He said a dozen vehicles, mostly two wheelers, were set afire.
Samajwadi Party and Congress MLAs held protests in the state assembly complex against the Citizenship (Amendment) Act. SP workers also defied the ban on protests in several districts, the party said. Their protests largely remained peaceful.
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Teachers from the Aligarh Muslim University, the scene of violence on Sunday, also took out a protest march. Shopkeepers in some areas of the city briefly downed shutters in support.
Traders in many markets shut shop early as reports of violence in the old city came in.
Police fired tear-gas shells in old Lucknow's Madeyganj area as protesters smashed vehicles parked outside a police post. About 20 people were taken into custody.
In Hasanganj area, policemen dodged stones hurled by protesters. They had a tough time tackling protesters in some other parts of the old city as well.
At Lucknow's Parivartan Chowk, close to the district magistrate's office, police faced brickbats and the van of a television crew was reportedly damaged.
Party sources said Uttar Pradesh Congress Committee president Ajay Kumar Lallu was also detained while leading a protest there.
The gates of the nearby KD Singh metro station were shut to prevent more protesters from gathering at Parivartan Chowk.
In Sambhal district's Chaudhary Rai area, a public bus was set ablaze and another damaged as a protest turned violent, District Magistrate Avinash K Singh said.
Some protesters also pelted stones at a police station there, he said.
"The internet services have been suspended as a precautionary measure to prevent rumour-mongering," he said.
In Mau, protesters hurled stones, triggering a large deployment of UP's Provincial Armed Constabulary (PAC).
Several Aligarh Muslim University teachers held a silent march, days after the institute witnessed violence when students protested against the new legislation that they say discriminates against Muslim.
The protesters, including several women teachers, marched from the AMU Teachers' Club to the Purani Chungi Crossing.
"We want to convey to the people of India that our struggle against the Citizenship (Amendment) Act will continue peacefully within the democratic framework of the system," AMU Teachers Association secretary Najmul Islam told PTI.
"We feel that we are fighting for the idea of India as envisaged by the founding fathers of the nation. This is not a struggle for the rights of any particular community," he said.
Earlier, MLAs from the opposition Samajwadi Party and Congress held separate protests at the legislative assembly complex.
The MLAs gathered at the Assembly building in the morning ahead of the sitting of the state legislature, raising slogans against the legislation.
An SP MLA climbed the main gate of the Vidhan Bhawan. Some Congress legislators came outside the complex, but headed back when stopped by the police enforcing the prohibitory orders.
The SP also held protests in Gorakhpur, Maharajganj, Basti, Siddharth Nagar and Kushinagar districts, where police detained a number of party workers.
The amended Act allows citizenship to Hindus, Christians, Sikhs, Buddhists and Parsis who entered India before 2015 after facing religious persecution in three neighbouring countries. The list excludes Muslims.