India's ruling Bharatiya Janata Party will face elections in five states beginning next month, according to a schedule released on Friday, at a time when its approval ratings are slipping and it is under pressure to deliver on economic growth.

State elections are important for Prime Minister Narendra Modi to be able to gain control of parliament's upper house, where members are indirectly elected by state legislatures.

A lack of a majority in that house has stalled Modi's economic reforms agenda and delayed passage of a key tax bill.

About 170mn people will be eligible to vote in the states of Tamil Nadu, Kerala and Puducherry in the south, and in Assam and the agrarian state of West Bengal in the east.

All these states are ruled by regional parties or Modi's top rival, the Congress party.

"The BJP's performance will be seen as a referendum on the central government... A poor showing, especially in Assam, could damage the image of the ruling party," said Sandeep Shastri, professor of political science at Benguluru's Jain University.

The BJP's best prospects are in Assam where it is fighting on an anti-immigration plank while it trails in the other four states.

A nationwide opinion poll published by the India Today magazine last month showed Modi's popularity was still holding up but his nationalist alliance would win with a sharply reduced majority if general elections were held now.

The Congress party would double its seat share, the poll showed. No surveys have yet been done for the five states electing new assemblies next month.

Modi is trying to tackle a deepening crisis in rural India, where two successive droughts have pushed farmers deeper into debt and forced dozens to commit suicide. Last year, he lost the big heartland state of Bihar.

To allow for security forces to be deployed in strength to safeguard the election, voting in the five states will take place in phases between April 4 and May 16, chief election commissioner Syed Nasim Ahmad Zaidi told reporters.

The results will be announced on May 19.

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