Millions of people in north-eastern India could lose their citizenship on Saturday in what could become the biggest exercise in forced statelessness in living memory.

Human rights experts have raised serious concern over the drive against suspected illegal immigrants in the border state of Assam, warning it could create a humanitarian crisis that disproportionately affects Muslims and the region’s poorest communities.

Around 30 million people in Assam have been forced to prove they are citizens by demonstrating that they have roots in the state dating to before March 1971. The list of those who have been deemed citizens will be released on Saturday.

Campaigners describe a system of callous bureaucracy and political interference that has torn families apart and left the most vulnerable facing spells in detention centres and unaffordable legal fees.

The United Nations special rapporteur on minority issues, Fernand de Varennes, said the exercise “raises quite a few red flags” and “may be considered to be a discriminatory process and approach”. De Varennes said the number of people potentially affected could make this the biggest exercise in statelessness since the second world war.

Shahibul Sikder, from Barpeta district in western Assam, is among the many people waiting to find out if his name is included. His family has lived in Assam since 1938, and his father, brothers and sister’s name were all included in a draft version of the list. His was the only name excluded, apparently because of a problem with the family records.

“You’re treated in your own land as a foreigner. It’s not just me, a lot of people are scared. I hope that my name will come,” said Sikder, a teacher. “The whole family is disturbed. It is not a small thing. Even to go to the foreigner tribunal costs a lot of money. [People] have been living in fear for so long.”

Halimun Nessa, 32, stands with her children and displays a photograph of her husband Rahim Ali, who committed suicide the day before his children were to appear in front of a NRC tribunal in Assam. Photograph: Anupam Nath/AP

The publication of the national register of citizens (NRC) on Saturday follows a four-year process that has caused anxiety across the state. Lawyers say people’s citizenship has been denied on the basis of minor anomalies such as a spelling error in documents produced decades ago.

About 4 million people were left off a draft list of citizens released last year, and it is not known how many will remain excluded this weekend.

The Hindu nationalist-led government of Narendra Modi, which supports the project in Assam, has pledged to roll the process out across the country. The home minister, Amit Shah, has previously promised to deport immigrants, describing them as “termites”.

The BJP-led Assam state also plans to build an additional 10 detention camps to house those declared to be migrants.

The ministry of home affairs said on Thursday that if a person was excluded from the register on Saturday, they would not automatically be declared a foreigner and would have 120 days to file an appeal.

It also said it would introduce legal aid. “Every individual left out from final NRC can appeal to foreigners tribunals, an increased number of which are being established,” the ministry said.

Campaigners say the system has created huge uncertainty for people affected, who fear their jobs, land, access to healthcare and their children’s access to education could all be at risk.

“The attitude of the authorities is completely callous,” said Teesta Setalvad, the secretary of Citizens for Justice and Peace, a group that has around 500 volunteers supporting affected communities.

Many people have struggled to gather the documentation required by officials, and to navigate the bureaucratic processes involved.

“The birth certificate became legally mandated only after 1969. There are a lot of people I know in India who don’t have their father or mother’s birth certificates. Are you therefore going to say they are not parents of that person and therefore not Indian?” said Setalvad. “It’s a nightmarish mess.”

The register is primarily targeted at people whom authorities describe as illegal immigrants from Bangladesh, which shares a border with Assam. There is significant resentment towards immigration in the state, and there was an anti-migrant movement in the 1980s.

Aman Wadud, a human rights lawyer, said many of those excluded from draft versions of the register came from families that had lived in India for generations. “They are born here, their fathers were born here, their grandfathers were born here.”

He said there were concerns about the decisions made by tribunals. “Foreigners tribunals should be more judicious and not arbitrary. There are definitely, it seems, political pressures. There’s an environment created to declare more people as foreigners.”

Separately from the register, the BJP is pursuing a citizenship amendment bill, which aims to give citizenship to religious group such as Hindus, Sikhs, Buddhists and others who are minorities in neighbouring countries – but not to Muslims.