Goalpara, Assam - Ali, 25, is an electrician working at India's largest detention centre currently under construction in Assam state's Goalpara district in northeast India.

As he takes a break from his work to rest in front of the centre's hospital block, a thought occurs to him.

"Today I am working here. Tomorrow, it could be a jail for my brother-in-law," he says. "It will ruin my sister's family."

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Ali's brother-in-law failed to make it to the National Register of Citizens (NRC), a list published in Assam this year which declared 1.9 million people as "illegal" migrants, who now face either detention in a camp like the one coming up at Goalpara, or deportation.

Spread around nearly 300,000 square feet (28,000 square metres or 2.8 hectares) of land, the detention centre in Goalpara's Matia village, 126km (78 miles) from state capital Dispur, can house 3,000 people.

The Goalpara detention centre can hold up to 3,000 people [Tawqeer Hussain/Al Jazeera]

The centre is situated in a remote area of Goalpara with open land on its three sides and a road linking it to the main city of Guwahati in the front.

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On one side, the road to the detention centre passes through what is known as the "ghost" mountain.

According to local residents, legend has it that ghosts used to rule the mountain centuries ago and no human was allowed to cross it.

"I feel it is the same situation here. Any person who goes to this detention centre will not come back," said Ghulam Nabi.

"How is it human to isolate a person from the population, from his family and put him behind these giant walls?" asked Nabi, pointing towards the high walls of the compound.

Besides a hospital, the centre will have a dining area, school, recreational centre, and two separate lodging facilities designated for male and female inmates.

"Male and female inmates will be kept in separate areas divided by a six feet red-coloured wall. There will be 13 male blocks of four storeys each and two female blocks of the same size," Rabindra Das, an engineer with Assam's police housing board and incharge of the construction of the detention facility, told Al Jazeera.

"The entire compound is surrounded by two walls, the inner being 20 feet high, followed by the outer wall six feet high," Das said.

As a security measure, the detention centre has six watchtowers for round-the-clock monitoring, supported by a 100-metre high-beam light.

Officials said the federal detention centre will be completed by April [Tawqeer Hussain/Al Jazeera]

According to officials at the construction site, the centre was sanctioned by India's federal home ministry in June last year and was supposed to be completed by December. However, the deadline has now been pushed to April this year.

"It is a central government project. We have to finish the entire construction by April," said Das.

India's other detention centres

While the government has not yet announced a nationwide NRC, a number of detention centres are coming up across the country.

In Assam, which has witnessed a movement against mainly Bangla-speaking migrants for more than four decades, at least six detention centres are already operational.

On December 3, India's Minister of State for Home Affairs, G Kishan Reddy, in a written response, informed the Parliament that an existing detention centre in Goalpara has 201 inmates, Kokrajhar has 140, Silchar 71, Dibrugarh 40, Jorhat 196, and Tezpur centre holds 322 inmates.

There have been nearly 100 deaths in these centres since 2008, including suicides by the inmates.

In July, another Minister of State for Home Affairs, Nityanand Rai, said all the states have been asked to establish detention centres according to a Model Detention Centre Manual prepared by the government.

A number of detention centres are being prepared across India [Tawqeer Hussain/Al Jazeera]

On December 22, the southern state of Karnataka opened a centre for undocumented migrants in Nelamangala, some 40km (27 miles) from the capital city of Bengaluru.

An existing government building with six rooms, a kitchen and a security room was turned into a detention centre which can house 24 inmates. Recently, two watchtowers and a compound wall were added to secure the area.

The western state of Goa inaugurated its first detention centre on May 29 last year, while Rajasthan has a centre located inside a federal jail.

Reports said a detention centre in the state of Punjab is expected to be completed by May this year.

In the national capital of New Delhi, a detention centre has been operational since 2006 and is run by the Foreigners Regional Registration Office (FRRO).

In the western state of Maharashtra, the previous BJP government identified a piece of land on the outskirts of the financial hub of Mumbai to build a detention centre.

However, current Chief Minister Uddhav Thackeray, who leads a coalition government with the main opposition Congress and other parties, recently assured the state's Muslims to not worry, indicating that his government may not follow the centre's order on establishing a detention centre.

Reports said the government of West Bengal state also identified two locations - near capital Kolkata and in North 24 Parganas district - to construct detention centres.

But Chief Minister Mamata Banerjee, a staunch critic of Prime Minister Narendra Modi, last week said: "Don't fall for rumours. I am ready to give my life but I will not allow BJP to set up detention camps in [West] Bengal, never."

Kerala, another Indian state governed by a left-wing coalition, also put on hold the identification of land for a proposed detention centre.

Though there are no official figures, India's powerful Home Minister Amit Shah, while addressing an election rally in September 2018, claimed the country has about four million undocumented migrants.

Shefali Hajong, whose name was excluded from the final NRC list in Assam, is a construction worker at the Goalpara detention centre [File: Anuwar Hazarika/Reuters]

Muslims fear nationwide NRC

Among the 1.9 million undocumented migrants who could not make it to the NRC list in Assam, nearly half were Muslims, according to a report by the United Against Hate group.

Now, India's 200 million Muslims fear the process will be implemented across the country by the Hindu nationalist Bharatiya Janata Party (BJP) to marginalise the community.

The passing of the contentious Citizenship Amendment Act (CAA) last month has aggravated such fears, leading to huge protests across the country and resulting in at least 26 deaths so far.

The CAA grants Indian citizenship to six religious groups, except Muslims, from the neighbouring countries of Pakistan, Bangladesh and Afghanistan, who came to the country before 2015.

Critics say the law violates India's secular constitution by making religion a basis for citizenship. Muslims, on the other hand, fear the CAA is a precursor to NRC aimed at making their nationality questionable.

Recently, Prime Minister Modi contradicted his home minister by claiming his government never considered a nationwide NRC.

"Since my government has come to power, since 2014 to now, I want to tell [1.3 billion] citizens, there has been no discussion on even the word NRC," Modi said at an election rally in New Delhi.

However, Modi's government has allocated almost $130bn for creating a National Population Register, which activists say will serve as a database before the NRC is implemented.

Congress leader Rahul Gandhi accused Modi of lying. "The RSS's prime minister is lying to Bharat Mata [Mother India]," Gandhi said in a tweet.

The RSS refers to the far-right Rashtriya Swayamsevak Sangh (or National Association of Volunteers), which draws its inspiration from European Nazis and mentors the ruling BJP.

BJP spokesman Sambit Patra told Al Jazeera that there is "no connection" between setting up of the detention centres and the NRC.

"Don't link it with Muslims. Detention centre is for foreigners who are in India illegally," he said.

But Tanweer Fazal, who teaches political science at New Delhi's Jawaharlal Nehru University was not convinced.

"It is an easily understood fact if a non-Muslim gets excluded from NRC, then CAA can be his saviour. So only Muslims are left to go to the detention centres," he told Al Jazeera.