"Voting began at 7 a.m. on a moderate pace amid tight security," the official told IANS here.
By-election is being held in Bellary (reserved), Mandya and Shimoga parliamentary constituencies and Ramanagara and Jamkhandi Assembly segments.
Voting will take place till 6 p.m. in the 6,543 polling booths across the five constituencies.
A total of 54.5 lakh electorate, comprising 27.2 lakh men and 27.3 lakh women, are registered to vote for the by-election.
As 51,131 voters were physically challenged, the poll panel has arranged vehicles to ferry them for voting from their homes and drop them back.
In all, 31 candidates are in the fray, including five from the opposition Bharatiya Janata Party (BJP), three from the Congress and two from the Janata Dal-Secular (JD-S) and 21 others as Independents or from regional outfits.
BJP's state unit President B.S. Yeddyurappa's son B.Y. Raghavendra, who is contesting from Shimoga Lok Sabha seat, was among the early voters in the constituency.
Vote counting in all the five constituencies will take place on November 6.
(With inputs from agencies.)