Opposition candidate Paul Hounkpe on Monday conceded defeat to favourite Romuald Wadagni in Benin's presidential election.

Wadagni, who oversaw a decade of growth as finance minister, had been the overwhelming favourite in Sunday's contest after being endorsed by outgoing leader Patrice Talon, who handed on the baton after two five-year terms.

Hounkpe offered "republican congratulations" to Wadagni, saying he noted a clear lead for his sole rival and was therefore acting with "responsibility."

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Official results were expected not before Tuesday, but Wadagni's ability to conjure economic growth in the face of jihadist attacks had given him a clear lead even if the eight million-strong electorate showed scant enthusiasm for either choice before them, notably in the cities.

In the capital, Porto-Novo, turnout was between a mere 20 and 40 per cent for some polling stations.

Hounkpe only made the contest with help from the majority of lawmakers to secure the required parliamentary endorsements to stand.

The main opposition The Democrats party did not field a candidate as its leader, Renaud Agbodjo, failed to secure sufficient endorsements.

By midday Monday, the economic capital Cotonou had generally returned to its usual bustling rhythms with shops and businesses reopening after having closed for polling day, an AFP journalist observed.

Earlier, the Economic Community of West African States (ECOWAS) election observation mission praised "a peaceful atmosphere" and "the smooth running of the election."