Indian Prime Minister Narendra Modi’s BJP party is leading in elections in the north-eastern state of Assam for the first time, early trends suggest.
The BJP is ahead in 58 of the 126 seats, while the Congress is leading in 27 seats, the Election Commission said.
Assembly elections were held in Tamil Nadu, Kerala, West Bengal and Assam and in the union territory of Pondicherry.
Official results are due later. Despite its early lead in Assam, trends show the BJP trailing in other states.
The Assam results have come as a shot in the arm for the BJP which swept the national polls in the summer of 2014 but has since suffered setbacks in important regional elections, including in the capital, Delhi, and in the northern state of Bihar.
Assam is ethnically diverse and prone to conflicts and the state has been governed by the Congress since 2001.
For these elections, the BJP tied up with local parties that support rights of local tribespeople and are opposed to illegal migration and, correspondents say, that worked in its favour.
In the eastern state of West Bengal, the regional Trinamool Congress party led by Chief Minister Mamata Banerjee is poised for a second term in power.
Her party is leading in 217 of the 294 seats, while a rival alliance of the Congress and left-wing parties is ahead in 70 seats.
In southern Tamil Nadu state, the regional AIADMK has secured a lead in 129 of the 234 seats, while its nearest rival, the DMK, is leading in 90 seats.
In Kerala, which has been traditionally ruled by either Congress-led governments or a coalition of left-wing parties, the Communist Party of India (Marxist) is leading in 57 of the 140 seats, while the ruling Congress is ahead in 22 seats.