Around 9% votes were cast in the first two hours, according to poll officials.
Security personnel, including those of the central forces, have been deployed in constituencies to ensure free and fair elections and micro observers have also been deployed at all polling centres, according to the election office.
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Video recording and photography would be conducted at all the polling centres.
The Assembly seats where bypolls are being held include Saharanpur city, Bijnor, Thakurdwara, Noida, Nighasan Lucknow east, Hamirpur, Charkhari, Sirathu, Balha and Rohania, as also in Mainpuri Lok Sabha seat which was vacated by SP supremo Mulayam Singh Yadav.
Eleven Vidhan Sabha seats felt vacant after 10 BJP MLAs and one of its ally, Apna Dal were elected to the Lok Sabha.
Arrangement of web casting has been made at 176 sensitive poling stations.
While BSP is not contesting the bypoll, Congress and SP have fielded candidates for all 11 assembly seats, whereas BJP is contesting for 10 and its ally Apna Dal for one.
In Mainpuri, BSP and Congress have not fielded their candidates. Here the contest is between Mulayam's relative Tej Pratap Singh and BJP's Shiv Singh Shakya.