Opinion polls put Prime Minister Narendra Modi (right) as the favourite but he faces a tough challenge from Rahul Gandhi (left), of the Gandhi-Nehru dynasty. — AFP Photo

NEW DELHI — India's gargantuan election, the biggest in history, kicks off on Thursday with Prime Minister Narendra Modi seeking a second term from the South Asian behemoth's 900 million voters.

Opinion polls put Modi, 68, as the favourite but he faces a tough challenge from not one but two scions of India's storied Nehru-Gandhi dynasty attempting to capitalise on his poor record on jobs and rural poverty.

Because of the vastness of India, the election will be held in seven phases, from the tea plantations of Darjeeling to the slums of Mumbai to the tropical Andaman Islands, and everywhere in between.

Security forces are on high alert due to the perennial danger of violence, with five people including a local lawmaker killed in an ambush by suspected Maoist rebels this week.

Thousands of parties and candidates will run for office between now and May 19 in 543 constituencies across the nation of 1.3 billion people, with results not due until May 23.

Some of the 1.1 million electronic voting machines will be transported through jungles and carried up mountains, including to a hamlet near the Chinese border with just one voter.

Phase one on Thursday sees some 142 million voters - including 7,764 transgender voters, eligible to register as such for the first time - able to cast ballots. — AFP