About 10 per cent voters cast their votes in the first three hours, poll officials said.
Polling began on a dull note at 7 am but later picked up. More voters were seen in villages than in urban areas.
The polling in all 1,778 polling stations spread over seven assembly segments will continue till 5 pm.
A total of 1,509,671 voters, half of them voters, are eligible to cast their votes. As many as 23 candidates are in the fray.
The Election commission has made elaborate arrangements to ensure free and fair polling. About 8,000 polling personnel including 738 micro observers have been deployed.
As many as 10,000 security personnel including central paramilitary forces have been deployed to ensure peaceful conduct of the polling.
State Chief Electoral Officer Bhanwarlal said the polling process was being monitored through webcasting at 626 polling stations. At the other centres, officials have arranged videographers to record the proceedings.
Telangana assembly speaker Madhusudhana Chary, Deputy Chief Minister Kadiam Srihari, Congress MP R. Anana Bhaskar and TDP leader E. Dayakar Rao were among the prominent people who cast their votes in the constituency.
Kadiam Srihari's resignation as the MP following his induction in the state cabinet led to the by-election.
Stakes are high for TRS, which has fielded P. Dayakar. The Congress has nominated former union minister Sarve Satyanarayana while P. Devaiah is the BJP candidate.
The Left parties have jointly fielded Vinod Kumar while Suryaprakash is the candidate of the YSR Congress Party.
Chief Minister and TRS president K. Chandrasekhar Rao campaigned for the party candidate in the by-poll which is being seen as a referendum on the state government's performance. Central leaders of Congress party also participated in the campaign. YSR Congress chief Y.S. Jaganmohan Reddy, who is leader of opposition in Andhra Pradesh, campaigned for his party candidate.
Counting of votes will be taken up on November 24.
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