Narendra Modi of the Bharatiya Janata Party (BJP) will be the next prime minister of India, with counting trends showing the pro-business Hindu nationalist and his party headed for the most resounding election victory the country has seen in 30 years.

Modi's landslide was welcomed with a thundering rally on stock markets and raucous celebrations at offices across the country of his BJP, where supporters danced, exploded fireworks and handed out sweets.

The BJP looked certain of a parliamentary majority, giving the 63-year-old former tea-seller ample room to advance economic reforms which were started 23 years ago by current Prime Minister Manmohan Singh but stalled in recent years.

Singh's Congress party suffered its worst ever wipeout, a big boost to Modi's goal of ending the dominance of the Nehru-Gandhi dynasty that has governed for most of the 67 years of independent India.

Singh congratulated Modi on Friday with a telephone call.

Crowds surged around Modi's car after he visited his mother's home in Gujarat. He sent a message saying "India has won," that instantly set a record as the country's most retweeted Twitter post.

"I'm so happy because all of India wanted a strong government," shouted software engineer Vinod Rai at the BJP's Delhi headquarters. Rai echoed the sentiments of millions of Indians who bought into Modi's promises of job creation and economic growth to satisfy a bulging youth population.

With more than six times the seats of its closest rival, Modi's is the most decisive mandate for any leader since the 1984 assassination of prime minister Indira Gandhi propelled her son to office. Since 1989, India has been governed by coalitions.

The BJP was winning in 278 seats of the 543-seat parliament, counting trends showed. An alliance led by the party was ahead in 337 seats, TV channel NDTV said.

MARKETS SOAR

Responding to the news, Indian markets got off to a roaring start, with the rupee breaking below 59 to the U.S. dollar, an 11-month high, and the benchmark stock index jumping 6 percent to a record high before paring its gains.

Betting on a Modi win, foreign investors have poured more than $16 billion into Indian stocks and bonds in the past six months and now hold over 22 percent of Mumbai-listed equities - a stake estimated by Morgan Stanley at almost $280 billion.

Unlike his predecessors, Modi will not have to deal with unruly partners as he implements reform. That could usher in profound economic changes, and he will try to replicate his success in attracting investment and building infrastructure in Gujarat, the state he has governed for more than 12 years.

"He can afford to have a smaller but stronger cabinet, that means a far more decisive government. He has been saying less government and more governance, we are really likely to see that," said Navneet Munot, Chief Investment Officer at SBI Funds management in Mumbai.

But with India's economy suffering its worst slowdown since the 1980s and battling high inflation, it will not be an easy task to meet the hopes of millions of Indians who have bought into the idea that Modi will quickly push their country onto the top table of global economic powers.

"It's important to be realistic about how quickly they can instigate change. It takes time to, number one, get economic reforms through the political machinery, and number two, it also takes a while before economic reforms actually have a positive impact," said Leif Eskesen, an economist at HSBC in Singapore.

DESIRE FOR CHANGE

India's election was the world's largest ever. Staggered over five weeks, a record of more than 500 million ballots were cast from the Himalayas in the north to the tropical south, with voters braving blistering heat for a record 66 percent turnout.

Since being named as his party's candidate last September, Modi has flown 300,000 km (186,000 miles) and addressed 457 rallies in a slick, presidential-style campaign that broke the mould of Indian politics.

Modi contrasted his humble roots with the cloistered life of privilege of his dynastic rivals. He ran circles round his slow-footed opponent Rahul Gandhi, 43, from the Congress party which his family has dominated since his grandfather Jawaharlal Nehru led India to independence from Britain in 1947.

Prime Minister Singh launched reforms in 1991 as finance minister that opened India's socialist economy to global capital, but his spell in the top job ended marred by corruption and a floundering economy amid mounting policy paralysis. He has already bid farewell to his staff after ten years in office.

The desire for change has been so strong that voters put aside concerns about Modi's Hindu-centric politics.

A dark chapter of violence against Muslims on his watch has mattered less and less to many, including a bulging middle class alarmed by dwindling purchasing power and job opportunities as the economy slumped to sub-five percent growth in the last two years.

Modi has promised that, if elected, he would take decisive action to unblock stalled investments in power, road and rail projects to revive economic growth.

Tax and labour market reforms, backed by a gradual opening up to foreign investment, would seek to create the 10 million jobs that Asia's third-largest economy needs every year to absorb young people entering the workforce.

(Additional reporting by Frank Jack Daniel, Rajesh Kumar Singh, Aditya Kalra, Rajesh Kumar Singh, Malini Menon and Tommy Wilkes in NEW DELHI, and by Sanjeev Miglani in AHMEDABAD, India; Writing by Douglas Busvine and Frank Jack Daniel; Editing by John Chalmers, Simon Cameron-Moore and Mike Collett-White)