Prime Minister Narendra Modi will be among tens of millions of people to cast ballots as India holds a 'Super Tuesday' of voting in its marathon election.
The 117 seats to be decided will be the biggest number of any of the seven rounds of the election being held over six weeks.
Some 190 million voters in 15 states will be eligible to take part, and candidates on the ballot will include Modi's arch-rival Rahul Gandhi, head of the opposition Congress party.
Modi, leader of the Hindu nationalist Bharatiya Janata Party, will vote in his home state of Gujarat. He ruled the western state for over a decade before leading the party to national power in a 2014 landslide.
This election is seen as a referendum on his five-year rule -- which has seen impressive economic growth but not the jobs that the BJP promised.
Gujarat sends 26 lawmakers to the Indian parliament and the right-wing BJP won all of those seats in 2014.
Modi will vote in the constituency where his close associate Amit Shah, the BJP president and key powerbroker, is contesting his maiden election.
Gandhi is standing in Wayanad in Kerala state, taking a risk as south India is considered a stronghold of regional parties.
The opposition party leader says contesting Wayanad is a sign of his commitment to southern India. His opponents say it shows he fears defeat in his traditional seat in the northern state of Uttar Pradesh.
Under Indian election law, candidates can contest two seats, though they can only keep one if they win both. Gandhi is also on the ballot for Amethi in Uttar Pradesh.
- Round three of seven -
Turnout was robust in the first two rounds of voting, on April 11 and 18, with around 70 percent of eligible voters taking part.
Heavy security has been put in place for voting, though violence has still been reported, with Maoist rebels carrying out bomb and shooting attacks.
Authorities have also bolstered security in the restive Kashmir valley ahead of voting on Tuesday in the region considered a hotbed of anti-Indian sentiment.
Election results are to be released on May 23 and analysts say Modi is not expected to see a repeat of the BJP's 2014 performance, when they won 282 seats.
Modi has capitalised on nationalist fervour that followed India's air strikes on Pakistan in February in a dispute over Kashmir.
India accused its neighbour of harbouring a militant group that claimed a deadly suicide bombing in Kashmir.
The fractured opposition, led by Congress, has sought to attack the government over employment, the economy and a debt crisis for Indian farmers.