Gujarat police disperse protesters during a demonstration against India's new citizenship law in Ahmedabad on December 19, 2019. SAM PANTHAKY/Getty

New Delhi — The protests in India against a controversial new citizenship law continued escalating Thursday. The crisis could become a watershed moment in the history of the world's largest democracy. Unrest has erupted in cities and towns across this vast nation since the government brought in the new law which, for the first time in India's 70 years of democracy, singles out people of one faith.

Critics, from constitutional scholars to politicians, historians and Bollywood stars, have derided the legislation as unconstitutional and anti-Muslim, and next month India's Supreme Court will take up a legal challenge against it. The Citizenship Amendment Act (CAA) paves the way for illegal immigrants from Afghanistan, Bangladesh and Pakistan to become citizens, unless they are Muslim.

At least eight people have died, hundreds have been injured and several hundred more detained — including some prominent figures — as the protests have spread across this South Asian nation of more than 1.3 billion people. As the unrest escalated, the government banned large gatherings in parts of Delhi on Thursday, and in the states of Uttar Pradesh and Karnataka, where the technology hub of Bengaluru is located.

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William Dalrymple, a renowned British historian who has lived in India for 35 years, told CBS News on Thursday that the government's actions have left him "very anxious for the country I love."

"How any government deals with any protests is an indicator of commitment to democracy," Dalrymple said. "India's strength comes from its diversity, its pluralism, and its tolerance... and the erosion of that is a cause of considerable concern."

Protesters hold placards during a demonstration against India's new citizenship law in Siliguri on December 19, 2019. DIPTENDU DUTTA/GETTY

"I hope the government realises its mistake and pulls back," he said, adding that the ban on protests was "a very, very worrying thing. I am gravely concerned."

"People from all walks of life, religion, castes and professions have come out to protest this time," prominent Indian author and activist Arundhati Roy told CBS News on Thursday. "It took this (new citizenship law) for people of India to realize that we are heading towards a very, very dangerous time in India."

Anger, arrests and deaths

The Hindu nationalist government of Prime Minister Narendra Modi, which pushed the Citizenship Amendment Act and then signed it into law, says the protests are driven by the political opposition. The government has struck a defiant tone in the face of the protests and says there's no question of rolling it back.

Eventually it will come down to the Supreme Court to decide whether the law goes against the fundamental rights of equality and religious freedom enshrined in India's constitution.

What began primarily as protests by students at a Muslim university in the capital and an area in the north with a large Muslim population has snowballed into a national movement supported by people from all faiths and walks of life.

On Thursday, hundreds of thousands of protesters took to the streets in at least 23 cities. Two new deaths were reported by hospital officials in the city of Mangaluru and one in Uttar Pradesh state, bringing the total death toll to nine.

Hundreds of people were temporarily detained in Delhi and the southern city of Bengaluru, where thousands defied the protest ban. The government also temporarily suspended phone and cellular data services in parts of Delhi. Seventeen subway stations were also shut to prevent people from reaching the protest sites.

Among those detained in Bengaluru was Ramachandra Guha, a prominent Indian historian and biographer of India's democracy and independence icon Mahatma Gandhi. Guha was dragged away by police while speaking to members of the press (see it happen in the tweet below).

Dalrymple called Guha's arrest "a turning point," which he said "feels like the beginning of a new emergency."

"When intellectuals of Guha's repute are targeted in this manner, this is a very worrying moment for any country," Dalrymple told CBS News.

Last week, the Delhi police stormed a university campus, injuring hundreds of students in a baton charge and firing tear gas shells inside classrooms and the library. The siege drew condemnation from several quarters and protests of solidarity by students at more than 20 universities across the country.

Bollywood star Priyanka Chopra, who featured in the U.S. series "Quantico," said: "In a thriving democracy, to raise one's voice peacefully and be met with violence is wrong."

Chopra is among a handful of Bollywood personalities who have spoken out against the new citizenship law and the use of force against protesters. Other superstars have been trolled online for keeping silent.

Sudden citizenship test

A sea of people gathered Thursday evening in Mumbai, India's business capital, carrying placards denouncing the new citizenship law and the National Register of Citizens (NRC), a separate scheme the government plans to roll out nationwide after a controversial launch in a single state.

The NRC will require everyone in India to prove their citizenship by showing family documents going back decades. Those who aren't able to produce the required evidence face possible detention in camps or deportation. About 1.9 million people failed the sudden nationality test when the NRC was rolled out in Assam state earlier this year.

Opponents say the citizenship law and the NRC are moves by the Modi government aimed at marginalizing the country's minority Muslim population and consolidating its backing among nationalist Hindus. About 200 million of India's 1.3 billion inhabitants are Muslim.

The combination of the new law explicitly singling out Muslims and the NRC could effectively strip millions of Muslims of their citizenship. Many people from the three neighboring countries covered by the CAA have lived in India for years, decades even, but they may be unable to prove their residency under the NRC criteria.

Under the new citizenship law, those from Bangladesh, Afghanistan and Pakistan will be able to regain their citizenship rights — unless they are Muslim.