Former school teacher Mayawati Kumari and 49 ministers took the oath of office in Lucknow, capital of Uttar Pradesh state, after her party stunned rivals and defied exit polls in a win hailed as a political milestone.

Mayawati's win has been attributed to her plea to voters to set aside intense battlelines of religion and caste in the impoverished state.

"My government will provide a rule free of injustice, crime, fear and corruption and which is oriented towards development," the 51-year-old leader told reporters at her first news conference after taking office.

"There will be development for all, but priority will be given to lower castes and those left behind," the chief minister said in reiteration of her winsome election campaign through which she stitched a "rainbow" alliance.