India has published a list that effectively strips about 4 million people in the north-eastern state of Assam of their citizenship.
India says the process is needed to identify illegal Bangladeshi migrants.
But it has sparked fears of a witch hunt against Assam's ethnic minorities.
Fearing violence, officials say that no-one will face immediate deportation.
The publication of the NRC on Monday comes amid popular anger over illegal migration into Assam, which shares a porous border with Bangladesh.
Proponents of the registry say it will help root out illegal Bangladeshi immigrants, but the move has prompted fears of possible deportation among Assam's hundreds of thousands of Bengali-speaking Muslims.
The decision to impose a state-wide register of citizens has drawn parallels with Myanmar's Rakhine State, where Rohingya Muslims have long faced persecution owing to their Bangladeshi ancestry.
Image credit: Getty Images