Indian police used tear gas and smoke grenades to disperse a crowd of thousands of protesters in India's capital of New Delhi on Monday as violence broke out over a new citizenship law just ahead of US President Donald Trump's maiden visit to the city.

New Delhi has been a hotbed of protest against the controversial new citizenship law and protesters have been camping out continuously in several parts of the capital for the last two months.

Hundreds of people supporting the new law clashed with those opposing it, with stone pelting from both sides.

The two groups have been clashing since Sunday and the people supporting the law were seen chanting “Jai Shree Ram”, amid heavy stone pelting from both sides, according to a Reuters witness.

“We are in support of the CAA. If they want to protest, they should go somewhere else,” a protester Amit said, giving only one name.

One police officer was killed in the violence, police spokesman Anuj Kumar said.

New Delhi’s highest elected official, Arvind Kejriwal, tweeted that the violence was “very distressing”.

A 400-meter stretch of road was strewn with bricks and stones after the clash on Monday. The New Delhi television news channel said authorities deployed para-military forces to defuse the situation.

The latest round of violence broke out just as US President Donald Trump began his maiden visit to India, addressing a mega rally in Indian Prime Minister Narendra Modi's home state of Gujarat on Monday.

Trump is scheduled to arrive in New Delhi later on Monday.

India's Citizenship Amendment Act, which eases the path for non-Muslims from neighbouring Muslim-majority nations to gain citizenship, has triggered weeks of sometimes violent protests against Modi's government.

The law is seen by its opponents as discriminating against Muslims and has deepened concerns that Modi's administration is undermining India's secular traditions.

Modi's ruling Hindu nationalist Bharatiya Janata Party denies any bias against the country's 180 million Muslims.

Protests, prayers in Indian capital ahead

As Trump was being feted by Modi in Ahmedabad on Monday, Hindu nationalist and communist groups held pro and anti-US street demonstrations in the capital.

A group of Hindu nationalists held a prayer meeting where they put a vermilion mark on the forehead of Trump’s photograph on a poster, blessing him, while a priest chanted Hindu hymns wishing Trump success in his endeavor for strong ties with India.

Vishnu Gupta, president of Hindu Sena, said “through a fire ritual we are invoking God to bless America and India”.

Elsewhere in New Delhi, dozens of supporters of the Communist Party of India carried a banner reading “Trump go back”. Anti-Trump street demonstrations also broke out in the cities of Gauhati in the northeast, Kolkata in the east and Hyderabad in the south.

Doraisamy Raja, the Communist Party’s general secretary, accused Modi of succumbing to US pressure on access to the Indian market rather than protecting India’s interests.

American dairy farmers, distillers and drugmakers have been eager to break into India, the world’s seventh-biggest economy, but talks between Washington and New Delhi appeared to have fizzled.

Still, the two leaders are scheduled to announce agreements at a news conference on Tuesday, capping off Trump’s two-day visit.