Indians began voting on Friday in the world's largest election as Prime Minister Narendra Modi seeks a historic third term on the back of issues such as growth, welfare, Hindu nationalism and personal popularity.

The vote pits Modi's Bharatiya Janata Party (BJP) against an alliance of two dozen opposition parties that promise greater affirmative action and more handouts while stressing what they call the need to save democratic institutions, Reuters reported. 

Friday's phase was the first and largest of seven, covering 166 million voters in 102 constituencies across 21 states and territories, from Tamil Nadu in the south to Arunachal Pradesh on the Himalayan frontier with China.

Almost a billion people in the world's most populous nation are eligible to vote in the entire exercise running through the peak of summer until June 1, with results set, opening a new tab for June 4.

Surveys suggest the BJP will easily win a majority even though voters worry about unemployment, inflation and rural distress in the world's fastest-growing major economy.

Critics accuse Modi's government and party of targeting India's 200 million minority Muslims to please their hardline Hindu base - charges both deny.