Over 1,000 personnel of central paramilitary forces have been deployed at a total of 314 polling booths across the assembly segment where by-election was necessitated by the death of sitting Samajwadi Party MLA Mahesh Narayan Singh.
Voting at all the polling stations is being videographed, officials said.
The Samajwadi Party, which is also in power in Uttar Pradesh, has fielded the deceased MLA's 26-year-old son Prashant Kumar Singh, hoping to gain advantage of the sympathy wave generated in the wake of the legislator's untimely demise at a Gurgaon hospital earlier this year.
In the 2012 assembly elections, Singh had defeated Rakesh Dhar Tripathi by a huge margin of about 45,000 votes.
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At that time Tripathi had fought as a candidate of fledgling outfit Pragatisheel Manav Samaj Party following his brief estrangement with the BSP.
However, now Tripathi has been wooed back by BSP supremo Mayawati, who has also assured him a Lok Sabha ticket as part of her renewed efforts to win back the support of Brahmin community.
While BJP has fielded Vidya Kant - a Brahmin, the Congress has given its ticket to Amrit Lal Bind.Brahmins and Binds are the most sizeable community in Handia.
However, in the assembly polls held last year, the combined vote share of the two national parties in Handia was less than five per cent of the total votes polled.