More than 87 million people across seven states are eligible to vote on Monday, including in the northern state of Jammu and Kashmir, where pro-independence activists have been seeking justice.
The activists have called for a boycott of the vote in Muslim-majority Kashmir. Protests turned ugly after at least one person was shot and wounded by Indian police there.
The seven-phase general election began on April 11. The last votes will be cast on May 19.
Monday’s voting includes some of the most electorally important regions in the north, including Uttar Pradesh, the state with the most members of parliament.
Voting is also taking place in strongholds of the main opposition Congress party in Uttar Pradesh, including the Amethi constituency of Congress leader Rahul Gandhi, and Rae Bareilly, which is represented by his mother, Sonia Gandhi.
Hundreds of additional troops have been deployed in Kashmir for the vote and polling staff and equipment was airlifted in.
Turnout was very low in the first hour of voting in the Himalayan region, an election official said.
Rights groups, including the UN rights office, say Indian troops are acting with "virtual immunity" in Kashmir, with laws shielding them from being sued.