Narendra Modi's party won a landslide victory in India's most populous state on Saturday in a massive vote of confidence for the prime minister halfway into his first term.
Modi's Hindu nationalist Bharatiya Janata Party won a surprise absolute majority in Uttar Pradesh in the north, which is home to 220 million people and seen as a key indicator of national politics.
Party leader Amit Shah called the win a "historic mandate" for the BJP, which also won a majority in the mountainous northern state of Uttarakhand, and claimed it would be able to form governments in Goa and Manipur.
"These results will set Indian politics in a new direction," he said at a press conference at the party's New Delhi headquarters.
"The faith that people have placed in the BJP and in Narendra Modi will pay off."
The BJP won 311 of the total 403 seats in Uttar Pradesh according to the figures on the election commission website and is expected to name its chief minister for the state on Sunday.
The party had been expected to perform well in UP, but few experts had predicted the scale of the victory in elections across five states viewed as a test of Modi's popularity after a controversial ban on high-value banknotes.
Modi's dominance has been largely unchallenged since he won the first overall majority in three decades in the 2014 general election on a pledge to wipe out corruption and kickstart the economy.
He already looks well-placed for re-election in 2019 over the centre-left Congress Party, which the BJP ousted from power in 2014.
In UP Congress ran in an alliance with the locally ruling Samajwadi Party (SP), but were trailing in a distant second.
Experts said the results showed Modi had succeeded in tapping into popular anger over corruption with the move, which was aimed at tackling tax evasion but also led to widespread chaos in a country where most transactions are cash-based.
"Modi played the populist card better than the other parties, including the ostensibly socialist parties like the SP and the Congress," said veteran political journalist Parsa Venkateshwar Rao.
"He sold the rhetoric of demonetisation as being anti-rich very well. I personally think demonetisation was a great folly, but in politics you can turn a bad economic decision into a great political play."
The BJP also made big gains in the northeastern state of Manipur, which shares a border with Myanmar and has long been plagued by separatist unrest.
The party won 21 of the 60 seats in the state, where it previously held none, behind Congress on 28.
Congress won in the northern state of Punjab, where it fended off a challenge from the fledgeling Aam Aadmi Party.
It was unclear who would form the next governments in Manipur and in Goa, where the Congress also led with 17 of the state's 40 seats, but fell short of a majority.
The results will strengthen the BJP's hand in parliament's upper house, where the lack of a majority has hampered its reform agenda.
In a tweet, Modi said he was overjoyed by the "unprecedented support from all sections of society" and congratulated party workers.
Deputy congress leader Rahul Gandhi congratulated the BJP on their UP win in a tweet and said his party would fight on.
Low-caste leader Mayawati, whose Bahujan Samaj Party was in third place in UP, said the results were "shocking" and asked the election commission to investigate the possibility voting machines had been tampered with.
Celebrations broke out at the BJP's headquarters in state capital Lucknow where euphoric supporters danced to drum beats and handed out sweets.
Many local voters said having the BJP in power both nationally and in the state assembly would be beneficial to UP.
"The state should now witness rapid development. Corruption and nepotism in governance would also come down," housewife Viti Kumar told AFP.
The BJP fared poorly in the last UP state elections in 2012, winning only 47 out of 403 assembly seats, but it clinched 73 out of 80 parliamentary constituencies in 2014 with Modi standing in the holy city of Varanasi on the banks of the Ganges.
Its win in Uttar Pradesh will have significant implications for the make-up of the Rajya Sabha -- the upper house of parliament.
The Rajya Sabha is based on parties' strength in the state assemblies, with the biggest states supplying the largest number of MPs.