There is no clear leader in Mexico's presidential election.
A quick vote based on sample figures had been expected to generate a result within hours of the polls closing.
But with the candidates, leftist Andres Manuel Lopez Obrador and conservative Felipe Calderon running neck and neck, officials decided to count all the votes before declaring a winner.
Officials said turnout was high after a lengthy campaign marked by bitterly-traded political insults and accompanied by a rise in drug violence.
