Early state election results show India's ruling Bharatiya Janata Party (BJP) trailing in three key states where they were in power.
The main opposition Congress is leading in all three states - Madhya Pradesh, Rajasthan and Chhattisgarh.
Correspondents say the losses are a predictable and likely temporary backlash against incumbent parties - and not a major worry for the BJP.
India will hold nation-wide parliamentary elections early in 2019.
Election results are also being declared for the southern state of Telangana and the northeastern state of Mizoram.
Regional parties - the Telangana Rashtra Samiti (TRS) and the Mizo National Front (MNF) - are leading in these states.
The Congress was widely expected to win in the northern state of Rajasthan, while the central state of Madhya Pradesh was always seen as a close contest between the two parties.
But early results in the central state of Chhattisgarh, where the Congress is ahead by a wide margin, have been the most surprising.
The BBC's Soutik Biswas in Delhi says the Congress's vastly improved performance in the three key heartland states will help change the perception that Modi's BJP is invincible, boost the morale of party workers and make the party more acceptable to sceptical regional allies in the run up the crucial general elections next year.
BBC Hindi's Nitin Srivastava who is in Rajasthan, has been posting photos of the starkly different atmospheres at the BJP and Congress party offices in the state.