Narendra Modi is garlanded by Defence Minister Rajnath Singh (L) and Home Minister Amit Shah (R) during celebrations following BJP's victory in New Delhi on Sunday. AP

Indian Prime Minister Narendra Modi's ruling party routed the main opposition in key heartland states as votes were counted on Sunday, months before national elections in the world's most populous country.

The victories in three of the five states that voted in November further boost Bharatiya Janata Party (BJP) and Modi.

The premier's party wrested control of Chhattisgarh and Rajasthan states from the opposition and retained Madhya Pradesh in a landslide despite a spirited challenge.

With the final votes still being counted, India's election commission on Sunday evening said that the BJP had won or was leading in 163 of Madhya Pradesh's 230 state assembly seats.

In Rajasthan, the BJP had 115 wins and leads in the 199 member legislature and the party was set to secure 54 of 90 seats in Chhattisgarh.

"Today's victory is historic, it is unprecedented," Modi said in a victory speech at the BJP headquarters in New Delhi on Sunday. "I bow to the people for their support. It is for our politics of good governance and developed India," he added.

Supporters of BJP celebrate early leads for the party in Rajasthan state elections in Jaipur. AP

The Congress defeated the regional BRS (Bharat Rashtra Samithi) party in the southern state of Telangana.

In the 119-member Telangana Assembly, the Congress was leading in 65 seats, while the BRS was ahead in 38. Votes in the small northeast Indian state of Mizoram will be counted on Monday.

Modi, who remains widely popular in his tenth year in office, flew across all poll-bound states in October and November to address tens of thousands of people in packed campaign rallies.

The states won by the BJP have about 190 million voters and elect dozens of members to the national parliament.

Addressing jubilant party supporters in the presence of the top BJP leadership at the BJP headquarters in Delhi, the prime minister said, "Today, the resolve of Aatmanirbhar Bharat has won, the idea of preference for the deprived has won, the idea of development of states for the development of the nation has won."

BJP leader and former CM Vasundhara Raje poses for a selfie with young party workers following leads for the party. AP

The prime minister extended his appreciation to the voters, calling the victories as historical and unprecedented. "The idea of 'Sabka Saath, Sabka Vikas' has won today," Modi declared, while acknowledging the immense love and faith for the BJP shown by the people.

"For me, four castes are important - Nari Shakti, Yuva Shakti, Kisan and Gareeb Parivaar," he said, highlighting the pivotal role women, youth, farmers and the marginalised families play in the nation's progress.

Expressing gratitude to Nari Shakti, Modi acknowledged their crucial role in ensuring BJP's success in the recent elections.

Agencies