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India started the world's largest election Monday, sealing international borders along its remote northeast while voters made their way past lush rice paddies and over rickety bamboo bridges and pot-holed dirt roads to reach the polls.

The country's 814 million electorate will vote in stages over the next five weeks — a staggered approach made necessary by India's vast size — to choose representatives to its 543-seat lower house of parliament.

The main Hindu nationalist opposition Bharatiya Janata Party led by prime ministerial hopeful Narendra Modi is seen as the biggest threat to the now-governing Congress Party and its allies.

Results from all 935,000 polling stations are expected on May 16.

Polls suggest Congress could be facing a drubbing thanks to corruption scandals and recent years of economic slowdown. The BJP, which has pledged economic renewal, is expected to do well but to fall short of a 272-seat majority. Its chief, Modi, has been credited for ushering in strong industrial growth in western state of Gujarat, where he has been chief minister for 11 years.

However, critics question whether the Hindu nationalist chief can be a truly secular leader over India's many cultures. And some economists have noted that the state's strong economy has not helped to lift common people out of poverty.

On Monday — the first of nine voting days — voters were selecting from candidates in five constituencies in the northeastern state of Assam and one in neighboring Tripura state.

For most voters in rural Assam, a state of 30 million people largely concerned with infrastructure and environmental damage, the two main national parties' focus on job growth and economic development have little urgency.

"As monsoon sets in, we get worried about our daily meals. We have been living on a mud embankment for years now after floods washed away our home and large part of our village," said Pulok Nath from the east Assam village of Lakhimpur.

Assam's highest elected official, Chief Minister Tarun Gogoi of the Congress Party, said he was confident of winning re-election.

"There is no Narendra Modi magic in Assam. The Congress has been winning every form of elections since 2001 in Assam, and we are going to repeat the performance this time," Gogoi said.

In the last general elections in 2009, Congress won seven of Assam's 14 parliamentary seats to the BJP's four, while regional parties won the rest.

Gogoi's 32-year-old son, running for office for his first time, said he was encouraged by the large number of politically engaged youths. With more than 65 percent of the country's 1.2 billion population aged under 35, many are expecting young voters to have a strong impact on the election.

"I am happy to cast my vote as a young man myself, I am extremely happy with the enthusiasm shown by the large number of young voters who have turned out to vote this time," Gaurav Gogoi said.

Several groups of separatist ethnic or Maoist rebels have threatened violence during the vote.

Authorities deployed 25,000 police and paramilitary troopers to guard polling stations on Monday. Helicopters were put on standby, and international borders with Bangladesh and Bhutan were sealed.

"Several ethnic insurgent groups and Maoist rebels may try violence to disrupt the polls. We are not taking chances," said Assam's police assistant director general, A. P Raut.

A state of diverse ethnicities, Assam has experienced several separatist insurrections since 1979, when the rebel United Liberation Front of Asom, or ULFA, was formed. Though one ULFA faction is in peace talks with the central government, another is still engaged in roadside bombings and ambushes on government soldiers.

Other ethnic rebel groups like the National Democratic Front of Bodoland are also cause for worry, with one faction threatening northern Assam politicians.

The northeast could also be affected by rebels inspired by Chinese revolutionary leader Mao Zedong, who have called for an election boycott and threatened to disrupt the vote. The Maoist rebels are active in 20 of India's 28 states.

On Thursday, the vote moves to five other northeast states — Nagaland, Mizoram, Manipur, Meghalaya and Arunachal Pradesh.