Indians are voting in the seventh and final phase of national elections, wrapping up a gruelling six-week-long campaign season.
Prime minister Narendra Modi's Hindu nationalist party is seeking re-election for another five years.
The voting on Sunday also covers Mr Modi's constituency of Varanasi, a holy Hindu city where he was elected in 2014.
He spent Saturday night at Kedarnath, a temple of Hindu god Shiva nestled in the Himalayas in northern India.
The last round of the elections includes 59 constituencies in eight states.
Up for grabs are 13 seats in Punjab and an equal number in Uttar Pradesh, eight each in Bihar and Madhya Pradesh, nine in West Bengal, four in Himachal Pradesh and three in Jharkhand and Chandigarh.
Counting of votes is scheduled for May 23.
In Kolkata, the capital of West Bengal, voters lined up outside polling stations since early morning to avoid scorching heat with temperatures reaching up to 38C.
Armed security officials stood guard in and outside the centres amid fear of violence.
While the election since April 11 has been largely peaceful, West Bengal state in eastern India is an exception.
Mr Modi is challenged here by Chief Minister Mamata Banerjee, who heads the more inclusive Trinamool Congress party and eyes a chance to go to New Delhi as the opposition's candidate for prime minister.
Australian Associated Press