The Indian Government has announced plans for a census to be held next year despite weeks of protests over a citizenship law that critics say is anti-Muslim.

Key points: At least 23 people have been killed in the unrest

At least 23 people have been killed in the unrest The Government invoked a British colonial-era law banning public gatherings

The Government invoked a British colonial-era law banning public gatherings Nearly 100,000 Sri Lankan refugees living in India are not eligible for citizenship under the new law

The protests began over a new law allowing Hindus, Christians and other religious minorities living in India illegally to become citizens if they could show they were persecuted because of their religion in Muslim-majority Bangladesh, Pakistan and Afghanistan.

It does not apply to Muslims.

Some protesters say the law is discriminatory against Muslims, while others fear it will lead to an influx of migrants.

Authorities say the updated National Population Register will be a comprehensive list of all residents, but critics fear it will further discriminate against Muslims, as "doubtful citizens" will be asked to prove they are Indian.

Prakash Javadekar, the information and broadcasting minister, told reporters that the census would begin this April, ending with a head count in February 2021 to prepare a national population register.

Authorities have taken a hard line approach to quell the protests, and 23 people have been killed in the unrest.

Authorities have taken a hard line approach to quell the protests, and 23 people have been killed in the unrest. ( AP: Aijaz Rahi )

Most of the deaths have occurred in the northern state of Uttar Pradesh, where 20 per cent of the state's 200 million people are Muslim.

More than 2,000 people have been arrested for protesting across India.

New York-based Human Rights Watch criticised the police and called on them to stop using unnecessary lethal force against demonstrators.

"The police get to the point of firing when someone's life is in danger," India's Interior Minister Amit Shah said.

"If in such a case the police don't use force, they are not fulfilling their duty."

'A bouquet of people'

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 3 seconds 1 m 3 s Protests continue in New Delhi as police ban public gatherings to quell demonstrations. ( ABC news )

Indian authorities stepped up security and shut down the internet in various places on Tuesday, while members of the ruling party planned marches in favour of the new citizenship law even as nationwide protests against it were escalating.

Prime Minister Narendra Modi defended the new citizenship law and said the Government had introduced reforms without any religious bias.

He accused the opposition of pushing the country into a "fear psychosis".

Hundreds of students marched Tuesday through the streets of New Delhi to Jantar Mantar, an area designated for protests near Parliament. They walked behind a huge banner that read, "We the People of India".

Vipul Kumar Chaudhary, a student, said the purpose of the march was to ensure that there was no discrimination on the basis of religion.

"India is a bouquet of people representing different religions. We want to preserve it," he said.

To quell the protests, the Government invoked a British colonial-era law banning public gatherings. Internet access has been blocked at times in some states.

The Ministry of Information and Broadcasting asked broadcasters across the country to refrain from using content that could result in violence.

The communication shutdown has mostly affected New Delhi, the eastern state of West Bengal, the northern city of Aligarh and the entire northeastern state of Assam.

Police banned public gatherings in parts of the Indian capital and other cities and cut internet services to try to stop the growing protests. ( AP: Altaf Qadri )

Law excludes Sri Lanka's Tamils

The new citizenship law excludes refugees from Sri Lanka, leaving nearly 100,000 Tamils living in India ineligible for citizenship.

This sparked concerns they may be forced to return to the island nation they fled during a decades-long civil war, many with no homes to return to.

Most of these refugees are Hindu or Christian, whose forefathers were born in India, said S Velayutham, an advocacy officer at the non-profit Organisation for Eelam Refugees Rehabilitation in the southern city of Chennai.

"Many were sent by the British as indentured labourers on Sri Lankan tea plantations, and hoped for a better life in India when they came here during the war," he said.

"Some 25,000 children were also born in the camps. They do not know any country but India, but now they may have no choice but to go to Sri Lanka."

Thousands of people were killed in Sri Lanka's civil war, which ended in May 2009 after nearly three decades.

Tens of thousands fled, or were forced from their homes, in the country's north and east, and many sought refuge in neighbouring India, particularly in Tamil Nadu.

The decision to exclude some marginalised groups from the CAA is "extremely disturbing", said Meenakshi Ganguly, South Asia director at Human Rights Watch, calling on the Government to revoke the CAA.

ABC/wires