Nearly 200m people in 141 constituencies are entitled to vote today.
Polling booths opened at 7am (2.30am Irish time), with voting in most districts set to end at 5pm.
This second phase of voting will complete the election in six states, including Andhra Pradesh and Orissa, where state assemblies are also being voted in.
However, they will have to wait until the middle of next month for counting of the votes.
For two of the states, it is only the second of five separate days during which voting will be taking place in at least some constituencies.
Security is tight in many areas where Maoist rebels have threatened to disrupt the voting.
Maoist attacks on polling stations during the first phase last week claimed at least 19 lives, including 10 paramilitary troopers and five election workers.
The month-long voting process concludes on 13 May, with the final results expected three days later.
