The polling for bypolls in eight assembly and four Lok Sabha constituencies began at 7 a.m. on Saturday.
In Tamil Nadu, nearly 7.54 lakh voters are expected to exercise their vote and decide the fate of 81 candidates in the fray in the three constituencies.
In Aravakkurichi, ruling AIADMK's V. Senthil Balaji will fight it out against the DMK's K.C. Palanisamy while at Thirupparankundram the AIADMK's A.K. Bose will take on the DMK's P. Saravanan.
In Thanjavur, the AIADMK's M. Rengasamy is pitted against the DMK's Anjugam Bhoopathy.
In Thirupparankundram, the by-election has been necessitated by the death of AIADMK's legislator S.S. Seenivel.
While there are other parties in the contest, the contest is mainly between the AIADMK and the DMK in Tamil Nadu.
In Puducherry's Nellithope, Congress leader V. Narayanasamy is contesting against AIADMK nominee Om Shakthi Segar.
The counting of votes will be held on November 22.
Meanwhile, voting for two Lok Sabha and one assembly seats in West Bengal is also underway.
An electorate of nearly 3,524,977, including 1,689,735 females and 38 from the third gender are eligible to choose their representatives from among 23 candidates vying for honours in Cooch Behar (Reserved-Scheduled Castes) and Tamluk parliamentary constituencies and Monteshwar assembly seat.
Voting for Shahdol Lok Sabha bypoll is also under way in Madhya Pradesh.
West Bengal: People queue up to vote for Cooch Behar lok sabha bypoll pic.twitter.com/0VHrRrnHkX— ANI (@ANI) November 19, 2016
Close to 1.7 million electors will seal the fate of eight candidates who are in the fray for the bypoll to Lakhimpur Lok Sabha constituency and Baithalangso assembly constituency in Assam on Saturday.
Assam: People queue up to vote for Lakhimpur lok sabha bypoll pic.twitter.com/soUuooTUON— ANI (@ANI) November 19, 2016
Polling for the two assembly seats in Tripura also began on Saturday morning amidst tight security measures.
The by-elections are being held in the scheduled caste reserve Barjala and Khowai assembly constituencies.