A diminutive former tax inspector is in the cross-hairs of Indian Prime Minister Narendra Modi's ruling party as it battles to take back power in Delhi state elections on Saturday.

Arvind Kejriwal, chief minister of the sprawling capital of 20 million since 2015, is standing for re-election - much to the chagrin of Modi's Hindu nationalist Bharatiya Janata Party (BJP), which is reeling from protests and a faltering economy.

Despite being swept to a second term in national elections last year, the BJP has not run Delhi since 1998 and it has campaigned heavily to try and unseat Kejriwal, who has been giving Modi a run for his money in appealing to the city's poor. Many ordinary voters see Kejriwal, 51, a co-founder of the Common Man Party, as "one of them", political strategist Amitabh Tiwari told AFP.

"He symbolises the power of the common man - that the common man can also contest and win elections."

The stakes are high for the BJP after it lost control of Maharashtra state, whose capital is Mumbai, late last year.

Economic growth is its slowest in six years, unemployment is high, inflation is accelerating and India has seen weeks of at-times violent demonstrations over a new citizenship law.

The law, making it easier for non-Muslim persecuted minorities to become Indian, has stoked suspicion that Modi wants to turn officially secular India into a Hindu nation, something he denies.