The world’s longest-ruling political party lost its six-decade grip on power as a former Roman Catholic bishop won the presidency of Paraguay.

The candidate for the ruling Colorado Party conceded defeat late last night after returns from the vast majority of polling stations showed Fernando Lugo had a commanding lead.

"We ask you never to abandon us. We'll make democracy together!" Mr Lugo told a cheering crowd of voters in Asuncion, the Paraguayan capital, to a deafening volley of firecrackers.

"We will give our best to ensure our people are respected and known from here on in for their honesty, not for their corruption."

The Colorado Party’s legacy of patronage and corruption however remain etched deeply into Paraguayan society, analysts warn.

Mr Lugo, a leftist who was swept to power by promising to help the poor and indigenous, is an untested newcomer to politics who forged his anti-Colorado coalition less than a year ago.

He has pledged to try to clean up the practices that have given Paraguay the reputation for being one of the most corrupt countries in South America and a haven for smuggling.

The grey-bearded, sandal-wearing former bishop, who quit the church 18 months ago in order to enter politics, is due to begin a five-year term of office on August 15.

He must steer the country through transition from one political party to another - a process not seen since the Colorado Party began its reign in 1947, before the communist parties in Cuba, China and North Korea took power.

The challenges he faces are tough: double-digit poverty, high illiteracy, 300,000 landless peasant farmers clamouring for help and the notorious corruption spawned by a huge informal economy in contraband goods.

Riordan Roett, head of Western Hemisphere studies at SAIS-Johns Hopkins University, said that Mr Lugo will have scarce chance to succeed and plenty of room to fail.

“The economic realities give the new team very little room to manoeuvre,” he said. “Good luck Bishop ... or you may find yourself in exile pronto.”

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