Front-runner Claudia Sheinbaum poised to become Mexico's 1st woman president

Media outlets and the ruling party declared front-runner Claudia Sheinbaum the winner of Mexico's presidential election after polls closed on Sunday, putting her on course to be the country's first woman president.

At least five exit polls showed Sheinbaum, a climate scientist and former mayor of Mexico City, winning the presidency, with pollster Parametria forecasting a landslide 56 per cent of the vote for the ruling Morena party candidate. Her main competitor Xochitl Galvez has not conceded and told her supporters to be patient for the official results.

Mario Delgado, head of the Morena party, told supporters in Mexico City that Sheinbaum had won by a "very large" margin.

On her way to vote on Sunday morning, Sheinbaum told journalists it was a "historic day" and that she felt at ease and content. Her victory represents a major step for Mexico, a country known for its macho culture, with her six-year term beginning Oct. 1 once results are finalized.

Mexico's largest-ever elections have also been the most violent in modern history, with the killing of 38 candidates. The deadly violence has stoked concerns about the threat of warring drug cartels to democracy. On Sunday, two people were killed at polling stations in Puebla state.

Sheinbaum, who has led convincingly in opinion polls over Galvez, will be tasked with confronting organized crime violence. More people have been killed during the mandate of outgoing president Andres Manuel Lopez Obrador than during any other administration in Mexico's modern history, although the homicide rate has come down over his term.

The violence was not limited to candidates. Two people were killed in violence at polling centres on Sunday as people cast their ballots.

Voting was suspended at one polling place after a person was killed in a shooting in Coyomeapan, a town in the state of Puebla, the state electoral authority reported in the afternoon. The state attorney general confirmed another death at a polling centre in Tlanalapan, also in Puebla.

The deadly violence stoked concerns about the threat of warring drug cartels to democracy.

Galvez, a senator who represents an opposition coalition comprised of the Institutional Revolutionary Party (PRI), the right-wing PAN and the leftist PRD party, chatted with supporters before casting her ballot early Sunday.

"God is with me," Galvez said, adding that she was expecting a difficult day.

There were long lines of voters outside polling places, even before they opened at 8 a.m. local time, with some reports of delayed openings.

"It seems like a dream to me. I never imagined that one day I would vote for a woman," said 87-year-old Edelmira Montiel, a Sheinbaum supporter in Mexico's smallest state of Tlaxcala.

"Before we couldn't even vote, and when you could, it was to vote for the person your husband told you to vote for. Thank God that has changed and I get to live it," Montiel added.