The result was the worst in history for the governing Indian National Congress party – the movement that won India's independence from the British in 1947 and has ruled India for most of the years since – and a humiliating rejection for Congress president Sonia Gandhi and her son Rahul Gandhi, who was the party's candidate for prime minister.

"It's a tsunami ... the BJP has levelled the Congress and this is a new era in Indian politics," BJP chief media spokesman Srikant Sharma told Fairfax Media.

"The Gandhi family is finished. They are no longer a force in Indian politics. India has moved past them, they are history," he said.

Rahul Gandhi's great-grandfather Jawaharlal Nehru was India's first prime minister, his grandmother Indira Gandhi was India's first female prime minister, and his father Rajiv Gandhi served as prime minister between 1984 and 1989.

Voters handed the BJP an outright majority of about 282 seats in the 543-seat lower house, the first party to achieve that since 1984, making it the most decisive result in a generation.

According to the latest projections, the BJP-led coalition known as the National Democratic Alliance will have 334 seats, giving the new prime minister a free hand to implement his pro-business, anti-corruption agenda.

The stunning performance by the BJP saw the party make gains in every corner of the country, shattering the Congress party,

The scale of the defeat for the Congress is catastrophic. At the last count, the Congress was facing a tally of as few as 47 seats. If the Congress ends up with less than 55 seats, it will not even qualify as the official opposition party.

Arnab Goswami, an anchor on Times Now, India's leading cable news channel, declared that Congress "has not been decimated, it has been completely and utterly destroyed".

The current Prime Minister, Manmohan Singh, called Mr Modi early on Friday afternoon to congratulate him on his party's victory. Dr Singh will resign on Saturday, while Mr Modi is expected to be sworn in as prime minister on May 21.

Mr Modi is yet to make a statement but tweeted that the result was a victory for the nation.

"India has won," Mr Modi said.

Senior BJP leader LK Advani, who is tipped to become the next parliamentary speaker, said the election was "unprecedented".

"The results in the Indian election show the mood today is against corruption and dynasty rule in the country. This kind of an election has never ever happened in the history of this country."

High on Mr Modi's to-do list are promises to unblock stalled investments in power, road and rail projects and to revive economic growth which has slumped to below 5 per cent - the lowest in a decade.

Another BJP leader, Balbir Punj, blamed Rahul Gandhi and Congress for "a campaign full of fear and hate" and said the party had got the result it deserved.

Congress leader Rajiv Shukla said the party had expected to win more than 100 seats and never in its worst nightmare had it imagined such a rout, claiming that Mr Modi had promised voters both "Jupiter and Saturn". "Mr Modi had sold a dream to India to which it has subscribed," Mr Shukla said.

"It's a crushing and devastating defeat," said another Congress leader, Ashwani Kumar.

Shellshocked Congress spokesman Satyavrat Chaturvedi said the failure was collective.

"Rahul Gandhi alone is not to blame," he said.

Despite the scale of the rejection for the mother-and-son combination, some Congress supporters at the party's Delhi headquarters were leading chants to draft Rahul Gandhi's sister, Priyanka Vadra, to lead the party.

With television networks declaring the result as early as 9.40am on Friday, less than two hours after counting began, jubilant BJP supporters across the country rushed onto the streets to celebrate.

Disenchanted by a decade of Congress rule that was marred by scarring corruption scandals and a sagging economy, voters are hoping Mr Modi will be able to use his mandate to break the gridlock that has made the current parliament the most unproductive in history.

Mr Modi has is expected to enact sweeping tax and labour market reforms, backed by a gradual opening up to foreign investment, and has promised to create 10 million jobs a year.

Watching the results on TV at his home in Gujarat, Mr Modi was due to meet his mother, 95-year-old Hiraben, and then travel to capital where he is expected to receive a hero's welcome.

"My blessings are there. The country will develop. My blessings are there," Hiraben Modi said.

The anti-corruption party Aam Aadmi, which attracted significant pre-election hype as a potential holder of the balance of power, failed to make an impact. The party was leading the count in only four seats.