With more than four hours into vote counting, the BJP-led NDA has crossed the majority mark of 148 seats in West Bengal, securing a lead in over 180 seats.
The incumbent Trinamool Congress (TMC) was restricted to 109 seats, while the CPI(M) led in just one seat.
TMC supremo and Chief Minister Mamata Banerjee, who was initially trailing in her Bhabanipur turf, regained the lead over BJP's Suvendu Adhikari by 898 votes after the third round of counting.
However, several TMC leaders, including ministers Udayan Guha and Sashi Panja, were trailing, initial trends showed.
In Cooch Behar district's Dinhata, minister Udayan Guha was trailing by 6,259 votes against BJP's Ajay Ray after four of the 24 rounds of counting.
In Kolkata's Shyampukur, minister Sashi Panja was trailing BJP's Purnima Chakraborty by 934 votes after two rounds of counting, with another 19 rounds left.
Aam Janata Unnayan Party (AJUP) chief Humayun Kabir was leading in the Nowda seat in Murshidabad district over his nearest TMC rival after the first round of counting, according to the Election Commission.
Kabir was leading by a margin of 2,890 votes over TMC's Sahina Momtaz Khan after the first round of counting.
The polls are seen as a crucial test for Chief Minister Mamata Banerjee and her TMC's bid for a fourth consecutive term, amid a stiff challenge mounted by the BJP. The CPI(M)-led Left Front and the Congress are also hoping to improve their tally after successive electoral setbacks.
Exit polls present a sharply divided picture, with some projecting a BJP edge while others forecast a comfortable return for the All India Trinamool Congress, underlining an uncertain and closely fought contest.
West Bengal BJP president Samik Bhattacharya said he was confident of a landslide victory, as counting of votes for the assembly elections began on Monday morning.
"People of the state have already rejected the Trinamool Congress government, and in a few hours, the overwhelming majority of the seats will confirm that in the fight between Mamata Banerjee and the people, people have rejected Mamata Banerjee," Bhattacharya said outside a counting centre in Kolkata.
The counting of votes for the state's 293 Assembly constituencies began at 8 am, with postal ballots taken up first in keeping with Election Commission norms.
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