Polling in the fifth phase of India's parliamentary elections was underway across seven states today with Congress president Rahul Gandhi, his mother and United Progressive Alliance chairperson Sonia Gandhi and Home Minister Rajnath Singh among the political heavyweights in fray.

The fifth phase covering 51 constituencies is the smallest in the seven-phase polling but assumes considerable significance for Prime Minister Narendra Modi-led Bharatiya Janata Party's re-election bid as it was in these states that the party had won most of the seats in the last national poll five years ago, reports our New Delhi correspondent.

The states where polling is being held today are Uttar Pradesh, Madhya Pradesh, Rajasthan, Bihar, West Bengal, Jharkhand and Jammu and Kashmir.

Uttar Pradesh, which elects 80 Lok Sabha members to the Parliament, will see polling in 14 constituencies today, including in Amethi where Rahul is pitted against federal minister Smriti Irani and Rae Bareli where Sonia is in contest against BJP nominee Dinesh Singh who quit the Congress and switched allegiance to the saffron party last year.

In Lucknow, the capital city of UP, Rajnath takes on debutant Poonam Sinha, wife of Bollywood actor-turned-politician Shatrughan Sinha who joined the Congress after leaving the BJP recently.

Uttar Pradesh has already voted for 39 seats in the previous four phases and polling in the remaining constituencies will be held in the last two phases on May 12 and 19. The results of the national polls will be declared on May 23, the correspondent reports.

While Sonia and Rajnath are expected to win easily, Rahul is facing a tough contest in Amethi where Smriti Irani had lost to him in 2014. The Congress chief also contested an additional seat Wayanad in Kerala state where polling was held last month.

The Samajwadi Party and Bahujan Samaj Party, which are fighting the elections in alliance in UP, has not fielded any candidate against either Rahul and Sonia. In fact, in a boost for the Congress on the eve of today's voting, BSP supremo Mayawati appealed to BSP and SP supporters to vote for Rahul and Sonia in Amethi and Rae Bareli.

The BJP and its other National Democratic Alliance (NDA) partners had won 41 out of the 51 (where fifth phase of polling was held today) seats in 2014.

The BJP won all 25 seats in Rajasthan and 27 out of 29 in Madhya Pradesh in 2014. But given the Congress victory in the 2018 assembly elections in the two heartland states just four months ago, a repeat by the BJP in the parliamentary polls appears unlikely.

In the ongoing elections, the BJP will also find it difficult to replicate its performance in UP where it had won 71 of the 80 seats in 2014 particularly because the Samajwadi Party and Bahujan Samaj Party are fighting in alliance representing a powerful combination of backward castes and Muslims.

The Congress, on the other hand, is looking to as many seats in in Rajasthan and Madhya Pradesh as possible building on the moment of win over the BJP in the assembly elections in the two states in December last year.

In four of the six states (Bihar, Jharkhand, Madhya Pradesh, Uttar Pradesh, West Bengal, and Jammu and Kashmir) barring Rajasthan where polling was held today, the BJP has either lost recent assembly election or is faced with a more united opposition.

Among the other most watched contests today are Jaipur Rural constituency in Rajasthan where federal minister of state for Information and Broadcasting Rajyavardhan Singh Rathore is in fray and Hazaribagh constituency in Jharhand where minister of state for Civil Aviation Jayant Sinha is in contest.

In Faizabad constituency in UP, the epicentre of the BJP's controversial Ram temple movement in adjacent Ayodhya at the site of razed 16th century Babri mosque, the BJP's Lallu Singh faces Congress candidate Nirmal Khatri who had won the seat in 2009 and SP's Anand Sen.

The temple issue did not find much traction in this year's election and even Modi avoided its mention during his election rally there.