Bypolls for two assembly seats are also being simultaneously held.
As many as 118 candidates are in the fray for the Lok Sabha seats of Sheohar, Sitamarhi, Muzaffarpur, Maharajganj, Saran, Hajipur and Ujiarpur. Also, 20 candidates are in contention in the bypolls for the two assembly seats - Chiraia and Maharajganj.
Additional Chief Electoral Officer R. Lakhshaman said over 53 percent of the electorate voted by 5 p.m.
"Large number of women came out of their houses and cast their ballots," he said.
The voting is underway peacefully despite apprehension of violence. "So far polls are peaceful with no report of violence," he said.
A polling agent of a political party was detained in Saran Lok Sabha seat by police following a complaint against him.
At several places in Sheohar, Ujiarpur, Muzaffarpur, Saran and Hajipur, villagers boycotted polls over lack of electricity and no roads.
Lakhshaman said despite the scorching heat, long queues of voters were seen. The electors were seen in some places even before balloting started at 7 a.m., he added.
"It is a good sign as large number of enthusiastic people have come out of their homes to cast their votes, particularly in the rural areas. The polling will pick up," he said.
Among the main candidates, Rashtriya Janata Dal candidate and former chief minister Rabri Devi is fighting against Bharatiya Janata Party's Rajiv Pratap Rudy in Saran constituency.
In Hajipur, incumbent MP and Janata Dal-United's Ram Sundar Das is locked in a battle against Lok Janshakti Party chief Ram Vilas Paswan.
Over 10 million electors are eligible to vote at 10,151 polling booths. A total 66,211 officials have been deployed to conduct the poll.