India’s prime minister, Narendra Modi, is on track for a historic landslide election victory that would cement the Hindu nationalist leader as the country’s most formidable politician in decades.

Modi’s ruling Bharatiya Janata party (BJP) had been expected to easily win a majority in coalition with smaller parties, but official results after nearly three hours of counting showed the party ahead in at least 290 seats, enough to claim an outright victory. Its main national opponent, Congress, was leading in just over 50 seats.

“Together we grow,” Modi said on Twitter as the results came in. “Together we prosper. Together we will build a strong and inclusive India. India wins yet again!”

This year’s polls, held over seven phases starting on 11 April, have been described as a contest for the soul of India, with Modi’s Hindu nationalist government pitted against a disparate group of opposition parties including the Congress, whose secular vision has defined the country for most of the past 72 years.

Votes from 542 lower-house constituencies – one fewer than usual after authorities discovered £1.3m in unaccounted cash in a south Indian party leader’s home and cancelled the poll there – started being counted at 8am local time (3.30am GMT), with results released progressively throughout the day.

Early results showed the BJP winning more than 20 seats in the crucial state of West Bengal – up from just two seats in 2014 – while holding off a co-ordinated challenge from opposition parties in the Hindi heartland states of north India, where its support had been expected to fall from the high watermark of five years ago.

Now it appears that high watermark was no aberration, and that Indian politics has likely entered a new era of Hindu nationalist hegemony fuelled by Modi’s extraordinary popularity.