Polling places opened at 8 a.m. and will close at 6 p.m.
The frontrunner in the polls is leftist Andres Manuel Lopez Obrador, the candidate of a coalition formed by the National Regeneration Movement (Morena), the Workers Party (PT) and Encuentro Social, Efe news agency reported.
Conservative Ricardo Anaya, the standard bearer of a coalition made up of the National Action Party (PAN), the Party of the Democratic Revolution (PRD) and the Citizens Movement, was in second place in most public opinion polls ahead of the election.
Jose Antonio Meade, the candidate of the governing Institutional Revolutionary Party (PRI), the Mexican Green Party and the Nueva Alianza, was in third place in the polls.
Jaime Rodriguez Calderon, known as "El Bronco" and the first independent candidate to compete in a presidential election in Mexico, occupied fourth place in most polls.
Lopez Obrador cast his ballot at a polling place in the capital and urged Mexicans to vote and "start the fourth transformation in the public life of the country" following "independence, the reforms and the revolution".
"We are deciding between more of the same or real change," the 64-year-old said.
The former Mexico City Mayor made fighting corruption one of the main issues in his presidential campaign.
"We are going to free the country of corruption, which is the principal problem in Mexico," Obrador said.
Anaya is expected to vote in Queretaro state, while is to cast his ballot in Coyoacan, located south of Mexico City.
Rodriguez will be the last to vote, casting his ballot at a polling place in Garcia, a city in the northern state of Nuevo Leon, around noon.
A total of 907 election observers from 60 countries have been deployed across Mexico.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
