Polling has opened for the fifth phase of India's marathon elections including in two constituencies in the vote-rich state of Uttar Pradesh where opposition Congress party president Rahul Gandhi and his mother Sonia Gandhi hope to retain their seats.

Voting began Monday amid tight security in Uttar Pradesh, where more than 25 million people are registered to cast ballots for 14 members of India's Parliament.

Rahul Gandhi is seeking re-election for a fourth consecutive time in Amethi. He is the son of assassinated former Prime Minister Rajiv Gandhi. Rajiv Gandhi's widow, Sonia Gandhi, is running from neighboring Rae Bareli.

Both constituencies are considered Congress party bastions.

India's multi-phase elections are seen as a referendum on Prime Minister Narendra Modi and his Hindu nationalist Bharatiya Janata Party, which controls Uttar Pradesh.