Sporadic violence-hit parts of Delhi overnight as gangs roamed streets littered with the debris of days of sectarian riots that have killed 33 people, police said Thursday.

Thousands of riot police and paramilitaries patrolled the affected northeast fringes of the Indian capital of 20 million people, preventing any major eruptions however.

The unrest is the latest bout of violence over Prime Minister Narendra Modi's citizenship law, which triggered months of demonstrations that turned deadly in December.

Sunil Kumar, director of the Guru Teg Bahadur (GTB) Hospital, said Thursday the hospital registered 30 deaths while the chief doctor at Lok Nayak Hospital said three people had died there.

"All of them (at the GTB) had gunshot injuries," Kumar told AFP.

Kishore Singh, medical superintendent Lok Nayak Hospital, told AFP that 10 people were still in a serious condition there.

The new fatalities -- up from 27 on Wednesday -- were all from the violence on Monday and Tuesday when mobs of Hindus and Muslims fought running battles.

The initial violence erupted late Sunday.

Groups armed with swords and guns set fire to thousands of properties and vehicles.

Homes, shops, two mosques, two schools, a tyre market and a fuel station were torched.

More than 200 people were also injured.

According to a list from the GTB hospital seen by AFP, the victims are a roughly even mix of Hindus and Muslims, based on their names.

Delhi police spokesman Mandeep Randhawa told AFP that there was "no major incident" overnight, while the city's chief fire officer Atul Garg said they received 19 distress calls.

"In last three days 230 calls were received by the department from the region that included major incidents of arson," Garg told AFP.

'Gun down traitors'

In December at least 30 people were killed, mostly in police action in the northern state of Uttar Pradesh, home to a significant Muslim population, after the citizenship law was passed.

Many of India's 200 million Muslims fear the citizenship law -- combined with a mooted citizens' register -- will leave them stateless or even sent to detention camps.

They and critics see Modi's right-wing ruling party, which is linked to once-banned militaristic Hindu group RSS, as wanting to turn officially secular India into a Hindu nation.

His party has denied the allegations but in recent weeks BJP politicians, including in an ugly recent campaign for Delhi elections, have called the demonstrators "anti-nationals" and "jihadists".

One, Parvesh Verma, said protestors "could enter houses and rape and kill your sisters", while another, Anurag Thakur, encouraged a crowd to chant "gun down traitors".

A call on Sunday by another BJP politician, Kapil Mishra, for "Hindus" to clear a northeastern Delhi sit-in protest is being seen as the spark for the current unrest.

On Wednesday a Delhi High Court judge, Justice S. Muralidhar, sharply criticised the police and called on them to investigate BJP politicians for inciting violence.

Muralidhar was transferred to another state court in a late-night order, prompting a social media storm. Law Minister Ravi Shankar Prasad insisted it was a "routine transfer".

On Wednesday the US Commission on International Religious Freedom, which advises Washington but does not set policy, voiced "grave concern" about the violence as President Donald Trump was visiting.

Anurima Bhargava, a commissioner appointed by Democratic House Speaker Nancy Pelosi, also expressed alarm at reports that Delhi police "have not intervened in violent attacks against Muslims."

Trump, asked at a news conference in the capital about the violence, said the issue was "up to India" and praised Modi's "incredible" statements on religious freedom.