Three people have died in India during protests, as more than 1,200 people have been detained for defying bans on demonstrations.
Arrests have taken place in several of the nation’s big cities as rallies continue a week on against what campaigners have called a “bigoted” new law.
Police have been accused of using excessive force as they try to clamp down on the protests.
The Citizenship Amendment Act entitles non-Muslims who are in the country illegally, to citizenship if they can prove they face religious persecution in Muslim-majority Bangladesh, Pakistan and Afghanistan.
It applies to Hindus, Christians and other religious minorities, but not Muslims.
Protesters say it is anti-Muslim, may cause mass migration and is an attempt by Prime Minister Narenda Modi to make India a Hindu stronghold. Mr Modi says it is a humanitarian gesture.
In an attempt to stop protests, a ban against large assemblies was rolled out across the country. More than 1,200 people were arrested in New Delhi.
Police say all the protesters were released later on Thursday.
Avinash Kumar, executive director of Amnesty India, said: “The Citizenship Amendment Act is a bigoted law that legitimises discrimination on the basis of religion.
“The people of the country have the right to protest against this law peacefully and express their views… [however] governments are clamping down on protesters by using repressive laws.”
Roadblocks have been put up while internet and phone lines have been deliberately disrupted by the authorities in large swathes of the country, including in the capital New Delhi.
A curfew was rolled out in areas of Mangalore, a city in southern Karnataka state. Police in the region fired warning shots, used tear gas and batons against protesters.
At least two people died there, according to the Press Trust of India news agency, while a third person was killed in Lucknow, in Uttar Pradesh state.
Meanwhile, India is building a detention centre capable of containing tens of thousands of people who will be determined to have entered illegally and who are unable to prove they are entitled to citizenship.