To be included on the list, people must provide documents proving they or their family members were residing in Assam prior to March 1971 - those who came after that date are kept off the list, making them illegal.
In response to criticism of the register, home minister Rajnath Singh said: "It is only a draft and not the final list, each one will be given a chance to make a claim of citizenship and any objections.
"Only after that will a final list be published. Some people are trying to create an atmosphere of fear."
Opposition parties have criticised the government and the NRC list. Bengal chief minister Mamata Banerjee said: "This is a means to divide the people of the country. People are being made refugees in their own country."
The indigenous Assamese people have long complained of large numbers of Bangladeshi Muslims coming into the state and changing its demography.
According to the census, Assam's population rose by 50% between 1970 and 1979, a rise that has mainly come from the Bengali-speaking Muslim population across the border. The state has a 167-mile porous border with Bangladesh.
This issue has triggered anti-foreigner agitation in the state. In February 1983, 2,000 immigrant Muslims were slaughtered in one night by machete-armed mobs in a brutal massacre in Nellie.
The incident led to the Assam Accord, which was supposed to solve the migration problem but the issue has been simmering since.
SKY News.