Mexicans voted for a new president Sunday in a contest dominated by women -- a historic first that was overshadowed by election day violence in the crime-plagued Latin American nation. 

Thousands of troops were deployed to protect voters, following a particularly bloody electoral process that has seen more than two dozen aspiring local politicians murdered.

Two people were reported dead on election day after attacks on polling stations to steal ballot papers.

Ruling party candidate Claudia Sheinbaum, a former Mexico City mayor and a scientist by training, had a 17 percentage point lead over her main opposition rival Xochitl Galvez in opinion polls ahead of the vote.

"It's a historic day. I feel very happy," Sheinbaum, 61, said as she left her home.

After casting her ballot, the presidential front-runner revealed that she had not voted for herself but for a 93-year-old veteran leftist, Ifigenia Martinez, in recognition of her struggle.

"Long live democracy!" Sheinbaum declared.

Galvez, a 61-year-old outspoken senator and businesswoman with Indigenous roots, said after voting that she expected a "huge participation" in the election.

"What I would like most is that no Mexican had to go abroad to look for opportunities," she added.

The only man running, centrist Jorge Alvarez Maynez, was trailing far behind in polling.

It means that, barring a huge surprise, a woman is almost certain to break the highest political glass ceiling in Mexico, where around 10 women or girls are murdered every day.

'Transformation'

"A female president will be a transformation for this country, and we hope that she does more for women," said Clemencia Hernandez, a 55-year-old cleaner in Mexico City.

"Many women are subjugated by their partners. They're not allowed to leave home to work," she said.

Daniela Perez, 30, said that having a woman president would be "something historic," even though neither of the two main candidates was "totally feminist" in her view.

"We'll have to see their positions on improving women's rights, resolving the issue of femicides -- which have gone crazy -- supporting women more," added the logistics company manager.

Nearly 100 million people were registered to vote in the world's most populous Spanish-speaking country, home to 129 million people.

Sheinbaum owes much of her popularity to outgoing President Andres Manuel Lopez Obrador, a fellow leftist and mentor who has an approval rating of more than 60 percent but is only allowed to serve one term.

In a nation where politics, crime and corruption are closely entangled, ultra-violent drug cartels have gone to extreme lengths to ensure that their preferred candidates win.

Hours before polls opened, a local candidate was murdered in a violent western state, authorities said, joining at least 25 other political hopefuls killed this election season, according to official figures.

In the central Mexican state of Puebla, two people died after unknown persons attacked polling stations to steal papers, a local government security source told AFP.

Voting was suspended in two municipalities in the southern state of Chiapas because of violence, local authorities said Saturday.

'Hugs not bullets'

Sheinbaum has pledged to continue the outgoing president's controversial "hugs not bullets" strategy of tackling crime at its roots. 

Galvez has vowed a tougher approach to cartel-related violence, declaring "hugs for criminals are over."

More than 450,000 people have been murdered and tens of thousands have gone missing since the government deployed the army to fight drug trafficking in 2006.

The next president will also have to manage delicate relations with the neighboring United States, in particular the vexed issues of cross-border drug smuggling and migration.

Sheinbaum had the backing of 53 percent of voters as campaigning drew to a close, according to a poll average compiled by research firm Oraculus.

Galvez was second with 36 percent. Maynez, 38, had just 11 percent.

Galvez often evokes her childhood story of growing up in a poor, rural town in central Mexico where she says she sold candy to help her family.

While millions of Mexicans have escaped poverty in recent years, more than a third still live below the poverty line in Latin America's second-biggest economy.

As well as voting for a new president, Mexicans will choose members of Congress, several state governors and myriad local officials.

In total, more than 20,000 positions are being contested.