India's opposition Bharatiya Janata Party (BJP) has picked up more popular support and remains best placed to lead a coalition government after a national election due by May, an opinion poll says.

The ruling Congress will slump to its weakest showing in parliament since independence in 1947, the Times Now-CVoter poll forecast indicated on Thursday, presenting a challenge to Rahul Gandhi, who is leading the party in its toughest election battle yet.

More than 700 million people are eligible to vote in the world's largest democratic exercise to choose a new government.

India, Asia's third largest economy, is growing at its slowest pace in a decade, choking off employment opportunities for tens of hundreds of youth who join the workforce each month.

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The BJP and its allies led by Narendra Modi will win 227 seats of the 543 at stake in the lower house of parliament, the poll said.

To rule a party requires the support of 272 members of parliament, and the BJP will have to gather support from regional groups who are also expected to do well in the election.

A survey conducted in October by the same polling agency soon after the aggressive Modi was named the party's prime ministerial candidate put his party's support at 186 seats.

The latest poll was conducted in a sample of just over 14,000 voters across 28 states between January 15 to February 8. Indian opinion polls have had a mixed record in the past, given the country's huge and diverse electorate.

Modi, a three-time chief minister of booming Gujarat state, has steadily pulled ahead, promising to revive the economy, cut red tape and fight corruption.

Rights groups and political rivals accuse Modi of failing to protect minority Muslims in the violence that gripped the state after a train carrying Hindu pilgrims was set on fire in 2002. Modi has denied any wrongdoing and a Supreme Court panel absolved him of any responsibility.

Source: Agencies