India's ruling Hindu nationalist party has made dramatic gains in elections in the eastern state of Assam but is trailing in four other states.

Data from India's election commission on Thursday showed that Prime Minister Narendra Modi's Bharatiya Janata Party and its allies will form the government in Assam, which has been ruled by the opposition Congress party for 15 years.

Local parties dominated the results In West Bengal, Tamil Nadu and Kerala states, while the Congress party was leading in Pondicherry. Voting in the five states was held over six weeks and counting took place Thursday.

State elections decide who controls the upper house of India's Parliament. While the BJP-controlled lower house is significantly more powerful, the upper house is crucial for passing legislation needed for economic reforms.