India's triumphant BJP declared "a new era" in the world's biggest democracy on Friday after hardline leader Narendra Modi propelled them to a stunning win, promising to revitalise the sickly economy.

Preliminary results at the end of the marathon six-week election showed the Bharatiya Janata Party (BJP) led by prime ministerial candidate Modi on track for the first parliamentary majority by a single party in 30 years.

Most of the poverty-wracked country's 1.2 billion people — more than half of whom are under 25 — have never witnessed such dominance having grown up in an era of fractious coalition politics. 

Modi, the 63-year-old son of a tea seller tainted by anti-Muslim riots in his home state of Gujarat in 2002, wrote on Twitter that "India has won. Good days are coming."

The stunning results exceeded all forecasts. Firecrackers exploded at BJP offices around the country, sweets were handed out to celebrate and painted elephants paraded in front of party headquarters. 

The triumph redraws India's political map, elevating the BJP to a pan-national power, handing Modi a huge mandate for change and heaping humiliation on the ruling Gandhi political dynasty.

The immediate change Modi will need to deliver is an improvement in the economy, growing at its slowest rate in a decade, and his commitment to the BJP's Hindu nationalist agenda will be closely watched by India's 150 million Muslims.

"It is dawn of a new era. The lotus has bloomed all over India now," said BJP president Rajnath Singh, referring to the flower symbol of his party whose previous all-time high was 182 seats in 1999.

"I appeal to my workers that even in this historic victory they maintain discipline and calm, against any section or people," he added, hinting at the fears of religious tensions.

Preliminary figures from the Election Commission showed the BJP winning more than the 272 seats required for a majority on its own in the 543-seat parliament, with victories by its allies taking it easily in excess of 330.