A man walks past damaged vehicles that were set on fire by demonstrators in Guwahati, India, on Thursday. Reuters

India moved thousands of troops into the northeastern state of Assam on Thursday after violent protests overnight against a new law that would make it easier for non-Muslim minorities from some neighbouring countries to seek Indian citizenship.

India's parliament set to vote on contentious citizenship bill

Police arrested dozens of people and enforced curfew on Thursday in several districts in India's northeastern Assam state where thousands protested legislation granting citizenship to non-Muslims who migrated from neighboring countries.

Soldiers patrol street following protests in Guwahati, India, on Thursday. Anuwar Hazarika/Reuters

Groups of protesters defied the curfew in Gauhati, the state capital, on Thursday morning and burned tires before police dispersed them.

Prime Minister Narendra Modi's Hindu nationalist government has said the so-called Citizenship Amendment Bill that was approved by parliament on Wednesday was meant to protect besieged minorities from Bangladesh, Pakistan and Afghanistan.

An Indian walks past a burnt bus during a protest against the Citizenship Amendment Bill in Gauhati, India. AP

Critics say it undermines the country's secular constitution by not offering protection to Muslims while others argue it will open India's northern states to a flood of foreigners.

Resistance to the bill has been the strongest in the tea-growing Assam state, where a movement against illegal immigrants from its neighbouring Bangladesh has simmered for decades.

Supporters of India's main opposition Congress party shout slogans during a protest against the Citizenship Amendment Bill, in Ahmedabad.

As India's upper house of parliament passed the bill, protests took place across India's northeast. In Assam, protesters defied a curfew, torching cars and tyres and chanting anti-Modi slogans.

Troops were moved in from other parts of India, including the troubled Himalayan region of Kashmir, state officials said, restoring calm to Assam's capital Guwahati, although protesters were back on the streets in other parts such as Morigaon, where they burnt tyres.

Mobile internet has been suspended in 10 districts in Assam for 24 hours until 7 pm Thursday, the government said in an order, adding that social media platforms could potentially be used to "inflame passions and thus exacerbate the law and order situation."

Police chase away demonstrators during a protest against Citizenship Amendment Bill, in Guwahati.

The turmoil in Assam comes just days ahead of an annual summit that Modi plans to host for Japanese Prime Minister Shinzo Abe there as part of his campaign to move high-profile diplomatic events outside Delhi to different parts of India, to showcase its diversity.

Protesters attacked the homes of Assam Chief Minister Sarbananda Sonowal and other members of the ruling Bharatiya Janata Party overnight, blaming them for playing politics with a region with a history of ethnic and religious tensions and by opening the floodgates to more outsiders.

"This a spontaneous public outburst," said Nehal Jain, a masters student in communications in Guwahati. "First they tell us there are too many illegal immigrants and we need to get rid of them. Then they bring in this law that would allow citizenship to immigrants," she said.

Of key concern is the legislation's new citizenship path for six religious groups including Hindus, Christians and Buddhists, but not Muslims, critics said.

The Indian Express said the law, which now only requires Presidential assent, unfairly targets India's 170 million Muslims.