Demonstrators react during a protest against a new citizenship law, in New Delhi.

Fresh protests rocked India on Monday as anger grew over new citizenship legislation slammed as anti-Muslim, after six people died in the northeast and up to 200 were injured in New Delhi.

The law fast-tracks citizenship for non-Muslims from three neighbouring countries.

Critics say it is part of Prime Minister Narendra Modi's Hindu nationalist agenda to marginalise the 200-million strong Islamic minority.

A burning bus is seen after it was set on fire by demonstrators during a protest.

Modi on Monday denied this, tweeting that the new law "does not affect any citizen of India of any religion", while accusing "vested interest groups" of stoking the "deeply distressing" unrest.

The UN human rights office said last week it was concerned the law "would appear to undermine the commitment to equality before the law enshrined in India's constitution", while Washington and the European Union have also expressed unease.

On Monday fresh protests took place including in Delhi, Chennai, Bangalore and Lucknow, where hundreds of students -- most of them Muslims, television pictures indicated -- tried to storm a police station, hurling volleys of stones at officers cowering behind a wall.

A student of the Jamia Millia Islamia university reacts during a demonstration after police entered the university campus.

Buses torched

Students gathered again at Delhi's Jamia Millia Islamia university on Monday, a day after police with batons fired tear gas and charged protesting students before storming the building.

The university's vice-chancellor Najma Akhtar said on Monday that 200 people were injured but police put the number at 39 students hurt with 30 officers also injured, one of them critically.

Police spokesman MS Randhawa said that four buses, 100 private vehicles and 10 police bikes were damaged, and that officers exercised "maximum restraint, minimum force" despite being "provoked".

He denied some media reports that police opened fire. 

A Muslim man holds a placard as he participates along with others in a peaceful protest against the Citizenship Amendment Bill.

Fellow student Shree Kumar said that the citizenship law was "against the Muslims.

It's against the ethos of India. It's against the secular ideas of India."

Authorities in Uttar Pradesh state cut internet access in some parts following clashes between demonstrators and police in Aligarh on Sunday that saw 21 people arrested, authorities said.

On the same day, Modi said the citizenship law is "1,000 percent correct" and that Muslims from Pakistan, Bangladesh and Afghanistan are not covered because they have no need of India's protection.

A demonstrator shouts slogans during a protest against a new citizenship law.

Modi blamed the Congress party and its allies of "stoking fire", saying those creating violence "can be identified by their clothes" -- a comment interpreted by some as referring to Muslims.

The new law is being challenged in the Supreme Court by rights groups and a Muslim political party, arguing that it is against the constitution and India's cherished secular traditions.

Agence France-Presse