An Indian election official shows an open Electronic Voting Machine (EVM) to polling agents at a counting centre in Ghaziabad on Thursday. Prakash Singh/ AFP

Indian Prime Minister Narendra Modi party claimed it had won re-election with a commanding lead in Thursday's vote count, while the stock market soared in anticipation of another five-year term for the Hindu nationalist leader.

Election Commission data by midafternoon showed the Bharatiya Janata Party leading in contests for 299 out of 542 seats in the lower house of Parliament, with its main rival, the Indian National Congress, ahead in 50 contests.

The data didn't indicate what percentage of the estimated 600 million votes cast over the six-week election had been counted. Although the final tally was not expected until Thursday evening at the earliest, BJP President Amit Shah claimed a victory.

Modi himself tweeted: "India wins yet again."

The election has been seen as a referendum on India's 68-year-old prime minister, whose economic reforms have had mixed results but whose popularity as a social underdog in India's highly stratified society has endured. Critics have said his Hindu-first platform risks exacerbating social tensions in the country of 1.3 billion people.

On the campaign trail, Modi presented himself as a self-made man with the confidence to cut red tape and unleash India's economic potential, and labeled Congress party president Rahul Gandhi, the scion of a political dynasty that lost power in 2014, as an out-of-touch elite.

Half a dozen exit polls released after voting concluded Sunday showed Modi and the Bharatiya Janata Party winning. A party or coalition needs a simple majority of 272 seats, or just over half the seats in Parliament's lower house, to govern.

"Mr. Modi's going to be the next prime minister, we are very assured of that," said Meenakshi Lekhi, a member of Parliament running for re-election in New Delhi. By midmorning, India's Sensex had jumped 2.3% to an all-time high over 40,000.

If BJP's lead holds, it won't need a coalition partner to stay in power. The BJP could also improve its position compared to 2014, when it won 282 seats, marking the first time in the party's history that it has two consecutive elections on its own.

World leaders, including Israeli Prime Minister Benjamin Netanyahu, Chinese President Xi Jinping and Sri Lankan President Maithripala Sirisena, congratulated Modi on Twitter.

Prime Minister Narendra Modi. File photo

An outright majority for Modi's party will likely embolden Hindu groups, who want to assert their dominance in the country, to the alarm of minority Muslims.

It would also allow Modi to push ahead with reforms to combat unemployment and rural distress that have persisted during his five years in power.

The mood was upbeat at BJP headquarters in New Delhi, with party workers cheering as TV channels reported a growing lead.

"It’s a huge mandate for positive politics and the policies of Narendra Modi," said GVL Narasimha Rao, a BJP spokesman. "It’s a huge win for India, we are humbled by the magnificence of this victory."

Congress leader Rahul Gandhi. File photo

Congress leaders were sombre.

"It's obviously not in our favour at all," said Salman Soz, a Congress spokesman. "We need to wait for the full results but right now it doesn't look good."

The National Democratic Alliance (NDA), led by the BJP, was ahead in 324 seats, with the opposition United Progressive Alliance winning in 111, after 10 a.m. (0430 GMT), about two hours after the counting of about 600 million votes began, Indian TV channel NDTV said.

NDTV and rival channel CNN News 18 have called the election for Modi's alliance.

The NDA's predicted margin of victory is much larger than surveys indicated in the run-up to the vote, when most polls showed it would be the largest alliance but would fall short of an overall majority.

Final results are due by Thursday evening.

Modi was under pressure when he began campaigning, losing three state elections in December amid rising anger over farm prices and unemployment.

However, campaigning shifted towards India's relationship with nuclear-armed rival Pakistan after a suicide car bomb killed 40 Indian police in the contested Kashmir region in February, to the benefit of the right-wing BJP, analysts said.

"National security became the discussion," said Harsh Pant, a political analyst at the Observer Research Foundation think-tank in New Delhi. "It allowed the BJP to shirk some issues where it was weak."

The BJP has also capitalised on the star power of Modi, a frenetic campaigner, as well as superior financial resources.

It outspent Congress by six times on Facebook and Google advertising, data showed, and by as much as 20 times overall, sources told Reuters this month.

Police guarded voting centres in West Bengal on Thursday, where campaigning had turned violent as the BJP tried to take seats from the Trinamool Congress, a powerful regional party.

Bombay Stock Exchange. File photo

The BJP was leading in 17 seats in the state, which sends the third largest number of lawmakers to parliament, significantly better than the two seats it won in 2014, NDTV said.

"Wherever we go people are talking about a BJP wave in Bengal," said Tapas Das, a taxi driver in the state capital, Kolkata.

"Everyone wants to see a change."

Indian stocks surged to historic highs as Modi headed for victory. The broad Nifty index was up 1.35% at 11,896.

The rupee headed towards 69.20 to the dollar, up from the 69.67 close on Wednesday, while the yield on the 10-year bond dropped 3 bps to 7.23%.

"For global investors, political stability and continuity is an important factor while taking a view on investing in any country," said R Sivakumar, head of fixed income at Axis Mututal Fund in Mumbai. "This will keep India on the radar of global equity investors."

Agencies