Morning walkers in almost all constituencies were among the first one to cast their votes.
The fate of 109 candidates will be decided in the by-polls that are being held in Gangoh, Rampur, Iglas (SC), Lucknow Cantonment, Govind Nagar, Manikpur, Pratapgarh, Zaidpur (SC), Jalalpur, Balha (SC) and Ghosi.
While eight of the seats in question were earlier held by the BJP and one by its Apna Dal ally, the Samajwadi Party and the Bahujan Samaj Party (BSP) had one each.
The BJP is seemingly at an advantage in the lackluster election campaigns by its political competitors.
The Samajwadi Party is contesting from all 11 seats across Uttar Pradesh, but its chief - Akhilesh Yadav - held just one election rally in the Rampur assembly constituency ahead of the by-elections. He was campaigning on behalf of party leader Tazeen Fatma after it was left vacant due to her husband, Azam Khan, moving to the Lok Sabha.
The Uttar Pradesh police have filed as many as 84 criminal cases against Azam Khan's family on charges ranging from land grab to theft over the last few months.
The BSP is also contesting all 11 seats on its own but its president Mayawati has not even campaigned for her candidates.
The Congress, which has got a new state party chief in Ajay Kumar Lallu and a new set of office-bearers, is also contesting from all 11 seats. No senior Congress leader has campaigned in the by-elections.
The BJP, on the other hand has campaigned rather vigorously with chief minister Yogi Adityanath leading the campaign. The party has targeted the opposition on national issues such as the abrogation of Article 370.
The bypolls in Uttar Pradesh were necessitated after a number of MLAs moved to the Lok Sabha by emerging victorious in the general elections earlier this year. The Assembly constituency of Ghosi fell vacant after sitting MLA Phagu Chauhan was appointed as the Bihar governor.
( With inputs from IANS )