At least 22 people have been killed in three days of clashes in New Delhi — that began during US President Donald Trump's first state visit to India — and the death toll is expected to rise, authorities say.

Key points: The new law makes it easier for non-Muslims from Afghanistan, Pakistan and Bangladesh to become citizens

The new law makes it easier for non-Muslims from Afghanistan, Pakistan and Bangladesh to become citizens Mobs beat people in the street and many of the injured were treated for bullet wounds

Mobs beat people in the street and many of the injured were treated for bullet wounds Witnesses saw both Hindus and Muslims being treated in hospital

Unrest over the new law began in December but the latest deadly clashes were the worst the capital has seen in decades.

Earlier, an official at Guru Teg Bahadur Hospital in New Delhi said 13 people had died there and more than 150 injured people, many of them with bullet wounds, had been treated.

India's capital has been a focus of unrest against the Citizenship Amendment Act, which makes it easier for non-Muslims from three neighbouring Muslim-dominated countries to gain Indian citizenship.

Under the law, religious minorities such as Hindus and Christians in neighbouring Bangladesh, Pakistan and Afghanistan, who have settled in India prior to 2015, will have the opportunity to become Indian citizens on the grounds that they have faced persecution in those countries.

On Tuesday clashes took place in multiple areas of north-east Delhi, just kilometres away from where US President Donald Trump and Indian Prime Minister Narendra Modi met for talks.

India's Junior Home Minister G Kishan Reddy told Asian News International the violence was "a conspiracy to defame India", at a time when Mr Trump was visiting the country.

Mr Trump told reporters he had heard about the unrest but did not discuss it with Mr Modi.

US President Donald Trump didn't comment on the new citizenship law after his talks with Indian Prime Minister Narendra Modi. ( Reuters: Adnan Abidi )

He declined to comment on the new law.

"I don't want to discuss that. I want to leave that to India, and hopefully they're going to make the right decision for the people."

In a separate speech on Monday, Mr Trump had praised India as a tolerant country.

"India is a country that proudly embraces freedom, liberty, individual rights, the rule of law and the dignity of every human being," he told a rally of over 100,000 people in Mr Modi's home state of Gujarat.

"Your unity is an inspiration to the world."

'The situation is very grim'

A car burns during the clashes in New Delhi. ( AP: Dinesh Joshi )

Local TV channels showed huge clouds of smoke billowing from a tyre market that had been set ablaze, and witnesses saw mobs wielding sticks and stones walking down streets, and stones being thrown.

"We have no weapons, but they are firing at us," said Mohammad Shakir, a demonstrator opposed to the law.

"This BJP is targeting Muslims. They want to turn India into a Hindu country."

ABC correspondent James Oaten said Muslims were now leaving affected suburbs because they no longer felt safe.

The Hindu-nationalist BJP denies any bias against India's more than 180 million Muslims.

An AP reporter saw a group of protesting Hindus shouting praise for Hindu gods and goddesses. Police fired tear gas to disperse them and a group of Muslims.

One police officer died after being hit by rocks. ( ABC News: James Oaten )

Witnesses at a local hospital spoke with both Hindu and Muslim victims who were injured in the violence on Tuesday.

Victims on both sides of the violence had suffered bullet wounds, and many had visible injuries on their heads and bodies.

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A fire department official said his teams were responding to more than a dozen calls over arson attacks, despite emergency measures prohibiting any gatherings in the violence-hit areas.

"We have sought police protection as our vehicles are being blocked from entering the affected areas. The situation is very grim," Delhi Fire Department director Atul Garg said.

Joint commissioner of police Alok Kumar said about 3,500 police and paramilitary officers had been deployed.

Police fired teargas and pellets to scatter demonstrators protesting against the citizenship law in the Jafrabad neighbourhood of north-east Delhi on Tuesday.

One police officer was killed in the violence after he was hit by rocks, Mr Kumar said.

Eleven other officers were injured by rocks as they tried to separate rival groups.

In New Jafrabad, residents patrolled the street with sticks and metal rods.

Two reporters with the local NDTV news channel were attacked and badly beaten by a mob.



Schools and multiple metro stations shut

A man is beaten on the streets of New Delhi during clashes over the citizenship law. ( Reuters: Danish Siddiqui )

On Monday police had used tear gas and smoke grenades but struggled to disperse stone-throwing crowds who tore down metal barricades and torched vehicles and a petrol pump.

Delhi Chief Minister Arvind Kejriwal appealed for calm.

"Whatever problems people have can be resolved peacefully. Violence will not help find a solution," he said.

India's Home Minister Amit Shah, who met local officials on Tuesday, urged political parties to avoid provocative speeches that could inflame protesters.

Schools in the north-east of the city were shut on Tuesday and at least five metro stations were closed. ( ABC News: James Oaten )

But, on Tuesday, after police cleared an anti-government protest site in north-east Delhi, BL Santosh, a leader from Mr Shah's party, called for a harsh response.

"The game starts now. Rioters need to be taught a lesson or two of Indian laws," he said in a tweet.

Schools in the north-east of the city were shut on Tuesday and at least five metro stations closed.

An announcement over a mosque loudspeaker urged protesters to stay non-violent and not to attempt to cross police barricades.

"We don't have a problem with the police, we are against the Government's law," the announcer said.

Muslims are now leaving the affected suburbs as they no longer feel safe. ( ABC News: James Oaten )

Reuters/AP