The voting began at 7 a.m. and will continue till 6 p.m., election department officials said here.
With the prevailing heat wave in Punjab, voters started queuing up early in the day to caste their votes.
Chief Electoral Officer S. Karuna Raju said that 1,72,676 voters will decide the fate of 12 candidates in this constituency.
The main contest is between the ruling Congress, Shiromani Akali Dal and the Aam Aadmi Party (AAP), making it a three-cornered contest.
Over 1,000 security personnel, including Punjab Police and Border Security Force (BSF), have been stationed in the constituency for smooth conduct of the voting.
The seat fell vacant following the death of sitting Akali Dal legislator Ajit Singh Kohar in February this year.
Kohar, a former minister, was elected five times from this seat. His son Naib Singh Kohar has been fielded by the Akali Dal this time.Congress candidate Hardev Singh Ladi had lost to Kohar by nearly 5,000 votes in the assembly elections in February last year.
The AAP has fielded Rattan SinghAas its candidate.The Congress came back to power in the state in March last year after a gap of a decade.