Mexican authorities on Wednesday were re-counting 54.5 per cent of the ballots cast in the country's presidential election, dpa reported. "This is the biggest exercise in openness, transparency and the highest publicity in Mexico's electoral history," said Edmundo Jacobo Molina, executive secretary of the Federal Electoral Institute (IFE). The re-count comes after centre-left candidate Andres Manuel Lopez Obrador challenged the preliminary results of Sunday's vote. He came in second, 6.51 percentage points behind the winner, centrist Enrique Pena Nieto. Lopez Obrador demanded a full re-count of the 49 million votes cast in Sunday's election. Pena Nieto, of the Institutional Revolutionary Party (PRI) that ruled Mexico without interruption from 1929-2000, got 38.15 per cent of the votes to the 31.64 per cent of Lopez Obrador, of the leftist alliance led by the Party of Democratic Revolution (PRD), according to the preliminary official count. There is no second round of voting in Mexico, and the final winner in Sunday's election is to be inaugurated for a six-year term December 1 to succeed outgoing President Felipe Calderon. Molina said the ballots from 78,012 polling centres are to be re-counted, out of a total of more than 143,000. Some 60 per cent of the ballots cast in the simultaneous legislative election are also to be re-counted. Lopez Obrador has claimed there are inconsistencies in 80 per cent of the voting centres. He alleged fraud and unfair use of the media, and accused the PRI of buying votes. The IFE has said Tuesday that it would re-count one-third of the ballots but then increased the proportion. Requirements for votes to be re-counted in a voting centre include the presence of obvious mistakes, a difference below 1 percentage point between the top two finishers, the fact that all votes in the precinct go to a single candidate or that the number of spoilt ballots is greater than the difference between the top two candidates. -- SPA