Indian politicians are expected to spend about $5bn on campaigning for elections next month - a sum second only to the most expensive US presidential campaign of all time - in a splurge that could give the floundering economy a boost.

India's campaign spending, which can include cash stuffed in envelopes as well as multi-million-dollar ad campaigns, has been estimated at $4.9bn (300bn rupees) by the Centre for Media Studies, which tracks spending.

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That is triple the expenditure the centre said was spent on electioneering in the last national poll in 2009 - partly a reflection of a high-octane campaign by pro-business opposition candidate for prime minister, Narendra Modi, who started nationwide rallies and advertising last year.

"They started much before, and they are also focusing on states where they are traditionally not strong. They are leaving no area untouched," said N. Bhaskara Rao, chairman of the Centre for Media Studies.

The campaign spending for this election could give a boost to the economy, which has been heading for its longest slump since the 1980s.

Economists have forecast a second year of growth below five percent in the financial year ending this month.

Candidate and party funding in India is opaque and the source of much of the spending is hard to ascertain, but the Centre for Media Studies and other transparency advocates say the main contenders have built up large war chests.

"This election spending largesse will help to boost Indian consumption expenditure over the second quarter of 2014, but this will be a temporary spike," said Rajiv Biswas, the Asia-Pacific chief economist at IHS Global Insight.

India's projected campaign spending is only rivalled by the $7bn spent by candidates, parties and support groups in the 2012 US presidential race, the world's most expensive, according to data provided by the US election commission.

Source: Agencies