West Bengal's ruling Trinamool Congress has established a comfortable lead with the BJP moving up to the second position by displacing the Left Front (LF) in the ongoing counting for the Kanthi Dakshin assembly seat by-polls on Thursday.

With counting for six out of the total 17 rounds complete, Trinamool candidate and former state Health Minister Chandrima Bhattacharya was ahead by over 20,000 votes over her nearest rival Sourindramohan Jana of the Bharatiya Janata Party.

Trinamool had won the seat in last year' assembly polls.

The Left Front nominated Uttam Pradhan of the Communist Party of India was running third.

In the 2016 assembly polls, the LF - which had a tie up with the Congress - took the second slot, and the BJP third.

Congress' Nabakumar Chanda was a distant fourth getting only around 1 per cent of the votes counted so far.

The seat fell vacant after the sitting legislator Dibyendu Adhikari was elected to Lok Sabha from the Tamluk seat in a by-poll last year.

Bhattacharya had lost from Dum Dum (North) seat in last year's assembly polls.