Modi thanked voters in Gujarat, his home state in India's west, and the northern Himalayan region of Himachal Pradesh, for backing the ruling Hindu national party in the local polls.
"I bow to the people of Gujarat and Himachal Pradesh for their affection and trust in BJP," Modi posted on his official Twitter account, using the initials of his Bharatiya Janata Party.
"I assure them that we will leave no stone unturned in furthering the development journey of these states and serve the people tirelessly."
BJP chief Amit Shah also called victory for the ruling party, saying Modi's development agenda had prevailed over "family politics", a reference to the Nehru-Gandhi dynasty that leads the main opposition Congress party.
India's Modi fights to protect home base in election
The BJP was on track to win 99 seats in the 182-seat Gujarat parliament as of 1015 GMT as counting continued, the Election Commission of India said.
That result would return the BJP to power for a sixth consecutive term in the bellwether state, but slash its majority from 115 seats in the last election.
The ruling party was also poised to wrest control of Himachal Pradesh from Congress, which recently elected Rahul Gandhi unopposed as its new leader to replace his mother Sonia Gandhi.
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