Indian Prime Minister Narendra Modi called for calm Wednesday after Delhi's worst sectarian violence in decades left at least 27 people dead and prompted demands for a military curfew.

This week's battles between Hindus and Muslims have seen mobs armed with swords, guns and acid raze parts of a northeastern district of the Indian capital.

The clashes, which also left more than 200 injured, were triggered by protests against a citizenship law seen by many critics as anti-Muslim and part of Modi's Hindu nationalist agenda.

20 people have died in sectarian violence in the Indian capital 20 people have died in sectarian violence in the Indian capital Photo: AFP / Sajjad HUSSAIN

They exploded into brutal violence on Monday and Tuesday, with residents forced to flee their homes after seeing dwellings destroyed, a mosque attacked and a tyre market and two schools set ablaze.

"I appeal to my sisters and brothers of Delhi to maintain peace and brotherhood at all times. It is important... calm and normalcy is restored at the earliest," Modi tweeted on Wednesday.

Delhi's chief minister, Arvind Kejriwal, a political opponent, called for the army to be deployed and for a curfew to be imposed.

The unrest in Delhi comes amid growing concerns at home and abroad about India's 200 million Muslims since Modi's Hindu nationalist BJP swept to a second term last year The unrest in Delhi comes amid growing concerns at home and abroad about India's 200 million Muslims since Modi's Hindu nationalist BJP swept to a second term last year Photo: AFP / Sajjad HUSSAIN

"Police, despite all (their) efforts, (are) unable to control the situation and instil confidence," Kejriwal tweeted.

Delhi Police spokesman Mandeep Singh Randhawa told reporters 106 people had been arrested.

The US embassy issued a travel warning advising citizens to exercise caution in the wake of the violence.

Sonia Gandhi, president of the opposition Congress party, has accused Modi's BJP party leaders of inflaming religious tensions Sonia Gandhi, president of the opposition Congress party, has accused Modi's BJP party leaders of inflaming religious tensions Photo: AFP / NARINDER NANU

Sunil Kumar, the director of Guru Teg Bahadur (GTB) Hospital where many of the wounded were taken, told AFP on Wednesday almost 60 had gunshot injuries and that 16 new patients were admitted on Wednesday.

Mobs were armed with swords, guns and acid Mobs were armed with swords, guns and acid Photo: AFP / Prakash SINGH

Twenty-five people died at GTB, while another two passed away at Lok Nayak Hospital Wednesday, medical superintendent Kishore Singh told AFP.

On Wednesday morning residents cleaned out the blackened interior of a trashed mosque, including a charred Koran, burned out during the violence in the Ashok Nagar area.

A video circulated on social media and verified by AFP showed men ripping off the muezzin's loudspeaker on top of the mosque's minaret and installing a Hindu religious flag.

Map of India showing New Delhi where at least 20 people have been killed after several days of rioting Map of India showing New Delhi where at least 20 people have been killed after several days of rioting Photo: AFP / STAFF

Locals accused the police of doing nothing to help -- or worse.

"We tried to make many calls to the police... that people are entering our neighbourhoods chanting 'Jai Shree Ram'," said Naeem Malik, referring to a popular Hindu chant.

"But police did not help us at all. We tried to save the women at the protest site but instead policemen started beating us up," he said, showing wounds on his leg and hands.

Elsewhere a firetruck tried to put out blazes from the previous night, the air thick with smoke from still-smouldering cars, motorbikes, shops and homes.

"They say we are not Indians, but we are Indians by blood," Farhat, 22, a student in Islamic studies, said in her father's shop as police looked on.

"There is no police in the streets at night, just during the day."

The area is home to mostly poorer economic migrants from elsewhere in India living in shanty neighbourhoods, and some fled on Wednesday ahead of more expected clashes.

The unrest comes amid growing concerns at home and abroad about India's direction and the future of its 200 million Muslims since Modi's Hindu nationalist BJP swept to a second term last year.

Sonia Gandhi, president of the opposition Congress party, on Wednesday accused BJP figures of giving "inflammatory speeches spreading an atmosphere of hatred and fear", including in Delhi city elections this month.

Since winning a second term, Modi's government has revoked the partial autonomy of Kashmir, India's only Muslim-majority state, and said it wants to conduct a nationwide citizens' register to weed out "infiltrators".

Together with the citizenship law, which fast-tracks claims for persecuted non-Muslim religious immigrants, the measures have stoked fears that Modi's master plan is to remould India as a Hindu nation, something he denies.

Modi, 69, was accused of doing nothing to stop religious riots in 2002 as chief minister of Gujarat when around 1,000 people died, mostly Muslims.

The latest flare-up in violence occurred as US President Donald Trump held talks with Modi in Delhi on Tuesday. The visit was not visibly interrupted.