Nine Indian states are gearing up to vote in the fourth phase of the gargantuan general elections that is to take place on Monday.

This time, voters from 72 constituencies will take part in the voting exercise. Polling will be held in Bihar, Jharkhand, Madhya Pradesh, Maharashtra, Odisha, Rajasthan, Uttar Pradesh and Bengal and Indian-occupied Jammu and Kashmir, NDTV reported.

Voting will start at 7am and conclude at 6pm (local times).

The opening phase of the mammoth exercise was held on April 11 when about 139.7 million people, including differently abled and transgender people, had cast their votes.

In the second round, millions had again cast their votes across 95 constituencies, albeit amid violence and protests. The third phase of the election was held across 15 states in which millions voted for 117 parliamentary seats. Among the states that took part in the election last week were Kerala and Gujarat, the latter being Indian Prime Minister Narendra Modi's home state and where he was the chief minister from 2001 to 2014.

With 900 million of India's 1.3 billion people registered to vote, it is the world's largest democratic exercise. Over the course of the election, 543 Lok Sahba seats will be decided from about a million polling stations across India.

Votes will be counted on May 23 and the results are expected the same day.

Modi's right-wing Bharatiya Janata Party (BJP), faces a significant challenge from regional parties and lead opposition Congress party of Rahul Gandhi.

Modi has run an aggressive campaign, playing to his right-wing, nationalist supporter base. However, he has come under criticism for failing to improve the economy and creating jobs.

Meanwhile, Congress has focused on concerns about rising unemployment and agrarian distress and is staking it campaign on a promise for a generous handout to India's poorest families.