(Reuters) - The first Indians cast their votes on Monday in the world's biggest election, with Hindu nationalist opposition candidate Narendra Modi holding a strong lead but likely to fall short of a majority.

Some 815 million people are registered to vote over the next five weeks as the election ripples out in stages from two small states near Myanmar to include northern Himalayan plateaus, western deserts and the tropical south, before ending in the densely-populated northern plains. Results are due on May 16.

Elderly women in saris and young men in jeans and polo shirts lined up outside a dilapidated sports center in Dibrugarh, a river town in the tea-growing state of Assam, one of two states to vote on Monday.

"We need a change, someone who will come and change the whole scenario," said handbag shop manager Ashim Sarkar, 35.

During high-octane campaigning at well-attended rallies the length and breadth of India, Modi has been promising to jumpstart a flagging economy and sweep out the Nehru-Gandhi dynasty that has ruled India for most of the period since independence in 1947.

"The proposals in the manifesto have the power to lift the nation from the ditch that it has fallen into, it has the power to give momentum to a nation that has stalled," Modi said at the New Delhi launch of his party's manifesto.

Turnout in the five constituencies in Assam that went to the polls on Monday was 75 percent. Voting ended at 5 p.m. and was peaceful, the chief election officer for the state told Reuters.