Six per cent polling was recorded in the high-profile Rampur assembly bypoll till 9 am on Monday, the Election Commission said.
By-elections to the Rampur assembly seat was necessitated after SP leader Azam Khan won general elections from the constituency earlier this year. Considered an SP bastion, Khan's wife Tanzim Fatima is the candidate from the Akhilesh Yadav-led party and is pitted against BJP's Bharat Bhooshan.
Uttar Pradesh Chief Minister Yogi Adityanath held three rallies in Bhooshan's favour. Akhilesh had also campaigned extensively in support for Fatima.
Ahead of the polling, Rampur District Magistrate Aunjaneya Kumar Singh visited different polling booths on Monday and inspected security arrangements.
"Special security measures, video cameras, web-casting etc are being used to ensure complete security. Micro observers and security teams on motorbikes have also been deployed in the constituency to maintain order," Singh told reporters.
The official also said that the administration will strictly deal with any attempts to create disturbance during polling.
By-polls in 51 assembly seats and two Lok Sabha constituencies across 18 states began today at 7 am, along with polling in Maharashtra and Haryana assembly elections. Counting of votes will take place on October 24.