Triumphant Hindu nationalist Narendra Modi promised to fulfil the dreams of 1.2 billion Indians as he propelled his party to a stunning electoral triumph Friday with the biggest winning margin for 30 years.

Preliminary results at the end of the marathon six-week election showed his Bharatiya Janata Party (BJP) on track for the first parliamentary majority by a single party since 1984.

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, an abrasive former tea boy tainted by anti-Muslim riots in his home state of Gujarat in 2002, promised to work for all Indians in a speech designed to sound inclusive amid suspicion of him among religious minorities.

"The heat of the election is over and the people have given their verdict, which says that we need to take India forward to fulfil the dreams of India's 1.2 billion people," he said at a rally in Gujarat.

The 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 in New Delhi.

"I want to take all of you with me to take this country forward... it is my responsibility to take all of you with me to run this country," Modi added in front of a crowd of thousands in his constituency of Vadodara.

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

Modi, 63, will face pressure to deliver a quick 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.

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.

"It is the 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.

- 'No magic wand' -

The Congress party, the national secular force that has run India for all but 13 years since independence, was set to crash to its worst ever result with fewer than 50 seats, a quarter of its tally in 2009.

It has headed two successive left-leaning coalition governments since 2004.

The disastrous showing is a severe blow to the Gandhi dynasty which runs Congress, particularly for 43-year-old scion Rahul, whose first performance as chief national campaigner will lead to acrimonious fallout.

Smiling despite the grim news, Rahul admitted in brief remarks that Congress had "done pretty badly".

"As vice-president of the party I hold myself responsible," he said.

Earlier in the day, a group of Congress supporters shouted slogans in support of Rahul's more popular sister Priyanka outside party headquarters.

Outgoing Prime Minister Manmohan Singh, who said in January that Modi would be "disastrous for the country" after "presiding over the massacre of innocents" during the riots in Gujarat, called to congratulate the BJP leader.

On financial markets, India's main Bombay Stock Exchange index closed up 0.9 percent after surging to a record high earlier in the day.

Investors and the wider public have rediscovered heady -- many say unrealistic -- optimism about the world's second-most populous nation after years of frustration about weak leadership, rising food prices and corruption.

"The economic problems are quite acute. There's no magic wand," D.K. Joshi, chief economist of credit rating agency Crisil, told AFP.

India is in the grip of stagflation -- growth has slumped to 4.9 percent from nine percent two years ago, and consumer inflation is at a wage-eroding 8.6 percent.

- Western boycott -

Modi has reinvented himself from a controversial regional leader accused of turning a blind eye to the religious riots in 2002, to an aspiring prime minister intent on helping India industrialise and create jobs.

His promises to revive the economy have won him corporate cheerleaders, while his rags-to-riches story and reputation as a clean and efficient administrator satisfy many Indians' desire for strong leadership.

While Prime Minister Singh, 81, was hailed by US President Barack Obama as a "wise and decent man", Modi presents an awkward prospect for Washington and other Western powers.

The bachelor, elected three times as chief minister in his home state, was boycotted by the US and European powers over the 2002 Gujarat riots that left around 1,000 dead.

He denies that he turned a blind eye to the bloodshed shortly after he came to power, and investigators have never found evidence of wrongdoing.

David Cameron, the prime minister of former colonial ruler Britain, called to congratulate Modi, and Prime Minister Nawaz Sharif from neighbouring Pakistan hailed an "impressive victory".