The Election Commission opened the ballot box at 8 a.m., tallying ballots from Nandigram, Rejinagar, Madurantakam, Dharapuram, Thattanchavady and Nagaon, seats vacated after winners opted to retain other constituencies.
In West Bengal, the bypolls carry political weight after the TMC split; the BJP fielded Hasirani Rath, mother of former aide Chandranath Rath, while the Trinamool factions jostle for control.
Tamil Nadu's contests bring former AIADMK legislators K. Maragatham Kumaravel and P. Sathyabama into the ruling TVK fold, with 27 and 30 candidates respectively, raising the risk of vote fragmentation.
Assam's Nagaon seat tests the ruling alliance's grip; the results, slated for 2 p.m., will either confirm the coalition's strength or signal a shift amid the SIR protests.