Some 139 million people were registered in 89 constituencies to vote in the latest round of a marathon contest pitting Modi against the Nehru-Gandhi dynasty-led ruling Congress party and a pantheon of satraps. Results are due on May 16.
Casting his vote in his home state of Gujarat, the leader whose pro-business policies have delighted investors brandished his party's lotus symbol and taunted Congress heavyweights for shying away from the fight.
"The prime minister himself is not fighting the election. The finance minister is not fighting the election. All its top leaders have run away," Modi said to cheers from a large crowd at the polling station in the state's largest city, Ahmedabad.
He snapped a "selfie" and posted the photograph on Twitter.
It is unusual for Indian politicians to give speeches after voting and Modi's opponents complained to the election commission that his use of the party symbol broke the rules.
Modi, who is standing in both the Gujarat town of Vadodara and the holy city of Varanasi, has shaken up Indian politics with an innovative campaign that has combined a massive social media outreach with up to five rallies a day. The 63-year-old has even appeared as a hologram campaigning in remote hamlets.
Opinion polls give a coalition led by Modi's Bharatiya Janata Party (BJP) a strong lead and predict the worst ever result for the ruling party, which led India to independence from Britain in 1947 and has dominated politics ever since.
But most surveys predict the BJP will fall short of the 272 seats needed for a parliamentary majority, meaning it will need to find allies. The size of the shortfall will determine whether a Modi government can pass free market reforms aimed at reviving the economy, or be constrained by protectionist allies.
The BJP "will most certainly beat the Congress," said Nida Ali of Oxford Economics.
"Now they are trying to maximize the number of seats they can get, so they are not hindered by other parties. If they can get a majority, that would help in decision-making."
Indian shares rose 6.5 percent in 2014 through Tuesday, outperforming the 0.5 percent drop in the MSCI emerging equities index, on expectations the industry-friendly BJP would score an emphatic win. But shares have cooled of late, as traders turn cautious ahead of election results.
India is sometimes described as a collection of countries united mainly by a common currency. The results of its elections are notoriously hard to predict, with block voting by caste and religion. Dramatic last-minute swings can confound experts, with opinion polls getting the result wrong in 2004.
In a reminder of the difficulties in converting Modi's popularity into seats, Arun Jaitley, a possible future finance minister, risks losing a contest in the state of Punjab over anger with the state government headed by a BJP ally.
The BJP's president, Rajnath Singh, also faces a tough fight in Lucknow, the capital of the big state of Uttar Pradesh, where voters lined up at schools despite the blazing summer sun on Wednesday.
The election remains Modi's to lose, however, and in recent days several senior Congress leaders have appeared to concede that prospects are gloomy. Finance Minister P. Chidambaram said on Monday "crucial mistakes" were made as public anger rose against corruption in 2010 and 2011.
The Congress party has governed for two terms and oversaw some of India's fastest ever growth, but lost popularity as the economy slowed and rampant graft was uncovered.
Chidambaram himself chose not to contest this election, a decision seen by many as a sign of weakness, while Prime Minister Manmohan Singh is retiring. A top adviser to Congress president Sonia Gandhi told the Times of India on Monday that the party would consider backing a non-BJP coalition led by a different party to stop Modi.
The party has since distanced itself from the comments.
"The Congress party and its allies will form the next government at the centre," said Shakeel Ahmed, a party general secretary.
But Congress has fought a lacklustre campaign, led by Rahul Gandhi, the great-grandson of India's first prime minister Jawaharlal Nehru. Gandhi's mother, Sonia, has also been a prominent campaigner, as has his sister. Some party leaders have even hinted a spell in opposition would be welcomed.
Modi wants to break the hold of the dynasty on Indian politics once and for all. He appealed to voters to put a strong government in place.
"The voting that has happened has achieved two things. One, the mother-son government is gone ... Second, a new government with a strong foundation will be in place," he said.