Polls opened at 7 a.m. local time (0130 GMT/UTC) on Friday, with seats in 21 states and Union territories around the country up for grabs in the first of seven phases of voting.
In all, 102 constituencies of the 545 in the Lok Sabha parliament are participating on Friday.
Queues formed before the polling stations opened at some sites.
Prime Minister Narendra Modi took to social media to appeal for record turnout.
"I especially appeal to young and first-time voters to vote in large numbers," he wrote. "After all, every vote counts and every voice matters!"
Indians head to polls in world's biggest election
First polls opened for India's 2024 general election on Friday, with country gearing up for seven phases of voting over a six-week period to accommodate some 968 million eligible voters.
There's more than 1 million polling stations set up around the world's most populous country and as many as 15 million poll workers will be involved in the giant democratic exercise.
According to most polls, incumbent Prime Minister Narendra Modi is the clear favorite for a third term, after landslide wins in 2014 and 2019.
Modi has been credited with taking India's economy to new heights and has promised to put India on track to become a developed country by 2047.
But critics say another term for the BJP could undermine India's status as a democratic nation, saying its 10 years in power has eroded the secular foundation of the country.
The last day of voting is scheduled for June 1 with counting and results expected on June 4.
How does the vote work?
The election will determine the composition of the 18th Lok Sabha or the lower house of parliament.
There are 543 contested seats, with two other seats nominated by the country's president. To rule, a party or a coalition needs a simple majority of 272 seats.
Whichever party or coalition wins the majority will lead the government and choose the next prime minister.
Votes are counted on a first-past-the-post basis like Britain's or that of the US. In each voting district, the candidate with the most votes claims the seat.
This means the share of the popular vote nationwide is not represented in seat allocation and winning an outright majority is easier than in countries with proportional representation.
Narendra Modi's Hindu nationalist Bharatiya Janata Party (BJP) won 303 seats last time out in 2019, plus another 50 for its various alliance partners that make up the BJP-led National Democratic Alliance (NDA).
The largest opposition party, Congress, could only claim 52 seats.
Modi seeking 3rd consecutive term
Prime Minister Narendra Modi is 73 years old and took office with his Bharatiya Janata Party (BJP) after 2014's election. Along with its partners it expanded its majority in 2019's vote.
Modi's tenure has coincided with India, now the world's most populous country, developing rapidly economically and also gaining influence on the global stage.
In overall terms, India is now the fifth largest economy in the world. While per capita wealth remains much more modest in global league tables, it too has risen sharply during Modi's tenure.
Modi has achieved staying in power by making Hindu nationalism acceptable to a nation that prided itself on pluralism and secularism.
His government has put the country's majority Hindu faith in the spotlight, for instance with the recent contentious Ram Temple inauguration at the former site of a mosque.
A recent Pew Research Group study pointed to very high approval ratings for Modi, roughly 80% positive and 55% very positive.
Congress asks people to vote to end 'inflation, unemployment, hatred and injustice'
India's main opposition party, the Indian National Congress, called upon people to vote in a post on X, formerly known as Twitter.
Writing in Hindi, Congress said: "Your one vote can put an end to inflation, unemployment, hatred and injustice," adding: "Make sure to vote."
