Electoral officials are counting votes in four Indian heartland states where the country's opposition Bharatiya Janata Party is expected to make strong gains against the nationally ruling Congress party.

The elections, held over the past month in Delhi, Madhya Pradesh, Rajasthan and Chhattisgarh, are seen as a test before next year's national elections.

The Hindu nationalist Bharatiya Janata Party, or BJP, has been waging a fierce campaign fronted by its prime ministerial candidate, Narendra Modi, in which he lambasted Congress over corruption scandals and soaring living costs.

Congress faces a likely upset when the results are announced later Sunday in the Indian capital, where a third upstart party campaigning against corruption pulled votes away from three-time Chief Minister Sheila Dikshit.