Tens of thousands of paramilitary personnel and police were deployed in India's border state of Assam on Friday, the eve of the publication of a citizenship register that could leave millions of people stateless, many of them Muslims.

For the last four years, residents of Assam have been scrambling to prove their identity in a court-ordered exercise after decades of campaigns by groups complaining about illegal immigrants from neighbouring Bangladesh.

On Saturday, authorities will release the final citizenship list. A draft last year left off four million people, raising the prospects of protests by people facing an uncertain future when the list comes out.

"We are on track to publish the final list on Saturday and all efforts have been made to ensure people have no difficulties in checking their names," a state official said.

Prime Minister Narendra Modi's government, which is supported by Hindu nationalists, has backed the citizenship test and said it could extend the exercise to other border states such as West Bengal.

Critics say the search for illegal immigrants in Assam has been largely directed at minority Muslims.

Police said 60,000 state police and 19,000 paramilitary personnel will be on duty on Saturday. The tea-growing state of Assam, with a population of 33 million people, has a history of sectarian and ethnic violence.

"All precautionary measures have been taken with security forces deployed in strength," said Assam police chief Kuladhar Saikia.

Residents had to produce documents proving that they or their families lived in India before March 24, 1971. Hundreds of thousands of people fled from Muslim-majority Bangladesh that year during its India-backed war of independence from Pakistan.

Hundreds of thousands of people who were left off the draft list have filed claims arguing that they are Indian.

The government says there will be a four-month period for people not on the list to file appeals with a tribunal.

Illegal immigrants will be sent to detention centres and eventually deported to Bangladesh, the government says.

But there are no facilities to hold large numbers of people and Bangladesh has made no commitment to accept people rejected by India.