Tens of millions of Indians have voted on the first day of a general election that is being seen as a referendum on Prime Minister Narendra Modi, reports BBC News.

Indians in 20 states and union territories cast their ballots in 91 constituencies.

The seven-phase vote to elect a new lower house of parliament will continue until 19 May. Counting day is 23 May.

With 900 million eligible voters across the country, this is the largest election ever seen.

Mr Modi's Hindu nationalist Bharatiya Janata Party (BJP) won a historic landslide in the last elections in 2014.

But critics say his promises of economic growth and job creation haven't met expectations, and India has become more religiously polarized under his leadership.

The BJP faces challenges from strong regional parties and a resurgent Congress party, led by Rahul Gandhi.