The ruling TMC was leading in Karimpur Assembly seat while the BJP was ahead in the Kaliaganj constituency of West Bengal after the first round of counting of votes for the by-polls, EC officials said on Thursday.
The Congress was leading in the Kharagpur Sadar seat, they said.
In Karimpur Assembly seat, TMC's Bimalendu Singha Roy is leading by a margin of 4,200 votes against his nearest BJP rival Jay Prakash Majumdar.
In Kaliaganj assembly segment, BJP's Kamal Chandra Sarkar is ahead of TMC's Tapan Deb Sinha by 1,600 votes.
Chittaranjan Mandal of the Congress-CPI(M) alliance is ahead of his nearest rival of Prem Chandra Jha of BJP by 980 votes in the Kharagpur Sadar seat.
Counting of votes began at 8 am on Thursday amid tight security in three Assembly seats of West Bengal where by-polls were held on November 25, Election Commission officials said.