NEW DELHI: Indian Prime Minister Narendra Modi's closest political ally has pledged to rid the capital of "illegal' immigrants if his party wins looming elections, in a forceful appeal to his party's Hindu constituency.

Interior minister Amit Shah said every unlawful migrant from neighbouring Bangladesh would be expelled from New Delhi "within two years" if his party succeeded in next month's provincial polls.

"The current state government is giving space to illegal Bangladeshis and Rohingyas," Shah told an audience of several thousand at Sunday's (Jan 26) rally.

"Change the government and we will rid Delhi of all illegals."

India shares a porous border stretching thousands of kilometres with Muslim-majority Bangladesh, and illegal migration from its eastern neighbour has been a hot-button political issue for decades.

There are no reliable estimates of the number of Bangladeshis living illegally in Delhi, a city to which millions have flocked in search of employment from elsewhere in India over recent decades.

Critics of Modi and Shah's Bharatiya Janata Party (BJP) accuse the party of using the issue as a dog whistle against Muslims to galvanise its Hindu-nationalist support base during elections.

Delhi, a sprawling megacity home to more than 30 million people, has been governed for most of the past decade by charismatic chief minister Arvind Kejriwal and his Aam Aadmi Party (AAP).

Kejriwal rode to power as an anti-corruption crusader a decade ago and his profile has bestowed upon him the mantle of one of the chief rivals to Modi and Shah's party.

His popularity has been burnished by extensive water and electricity subsidies for the capital's millions of poorer residents.

But he spent several months behind bars last year on accusations his party took kickbacks in exchange for liquor licences, along with several fellow party leaders.

Kejriwal denies wrongdoing and characterised the charges as a political witch-hunt by Modi's government, and despite resigning as chief minister last year vowed to return to the office if his party won re-election.

The BJP has led a spirited campaign in its efforts to dislodge Kejriwal's party ahead of the Feb 5 vote.

Modi is expected to make a pilgrimage to the ongoing Kumbh Mela, the biggest festival on the Hindu calendar, to bathe in the sacred Ganges river on the day of the Delhi assembly vote.

Results of the election will be published on Feb 8.