Mexico's campaign season came to a bloody end as a gunman shot dead an aspiring mayor at a rally on Wednesday, days before the country is expected to elect its first woman president. 

His murder brings the number of candidates who have been murdered to at least 23 during what has been a particularly violent electoral process in the Latin American nation, according to an official count.

Alfredo Cabrera, a mayoral candidate for an opposition coalition, was gunned down in the southern state of Guerrero, causing chaos and panic among people attending the rally.

Cabrera's murder was captured on camera, with the footage showing him smiling and flanked by fans before he was shot several times.

The state prosecutor's office said that "the alleged assailant was killed at the scene." Three people were also injured and two others detained, according to witnesses.

Cabrera belonged to the same opposition coalition as presidential candidate Xochitl Galvez, who expressed indignation over his murder.

"He was a generous and good man," she wrote on social media.

The Institutional Revolutionary Party (PRI), part of the opposition coalition, accused the government of having "not made even the slightest effort to guarantee the safety of the candidates."

Cabrera's death came just one day after a mayoral candidate in the central Mexican state of Morelos was murdered, while another one was wounded by gunfire in western Jalisco state.

Last week, nine people were killed in two attacks against mayoral candidates in the southern state of Chiapas. The two candidates survived.

Earlier this month, six people, including a minor and mayoral candidate Lucero Lopez, were killed in an ambush after a campaign rally in the municipality of La Concordia, neighboring Villa Corzo.

One mayoral hopeful was shot dead last month just as she began campaigning.

Around 27,000 soldiers and National Guard members will be deployed to reinforce security on election day.

New leader will face crisis of cartel violence

Tackling the cartel violence that has convulsed Mexico and turned it into one of the most dangerous countries in the world will be among the major challenges facing the next leader, along with managing migration and delicate relations with the neighboring United States.

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.

Barring a major upset, a woman appears almost certain to be elected leader of the world's most populous Spanish-speaking country when millions of Mexicans vote on Sunday.

Frontrunner Claudia Sheinbaum, from the ruling Morena party, ended her campaign with a rally in the capital's main public square.

"We're going to make history," Sheinbaum told the cheering crowd.

"I say to the young women, to all the women of Mexico -- colleagues, friends, sisters, daughters, mothers and grandmothers -- you are not alone," the 61-year-old said.

Sheinbaum has pledged to continue outgoing left-wing President Andres Manuel Lopez Obrador's social programs and strategy of tackling crime at its roots -- a controversial policy that he calls "hugs not bullets."

At her closing rally in the northern city of Monterrey, Galvez promised a tougher approach to cartel-related violence.

"You will have the bravest president, a president who does confront crime," she said.

Galvez accused Lopez Obrador of implementing "a security strategy where hugs have been for criminals and bullets for citizens."

Woman poised to be next president

Sheinbaum, a former Mexico City mayor and a scientist by training, enjoys a sizable lead in the polls with 53 percent of voter support, according to research firm Oraculus.

Galvez, a center-right senator and businesswoman with Indigenous roots, is second with 36 percent.

The only man running -- long-shot centrist Jorge Alvarez Maynez -- has 11 percent.

Thousands of Sheinbaum's supporters massed Wednesday to hear her speak, with many wearing purple -- the color of the ruling party.

"The people have woken up. We don't want the old governments to rob us anymore because the poor come first," said Soledad Hernandez, a 23-year-old housewife from the southern state of Oaxaca.

Sheinbaum owes much of her popularity to Lopez Obrador, widely known as AMLO -- a close ally who has an approval rating of more than 60 percent but is only allowed to serve one term.

"People from the countryside had nothing and now they're better off with AMLO," said Maria Isabel Zacarias, 55, a street food seller who came from the south to hear Sheinbaum speak.

Bertha Diaz, a 71-year-old Galvez supporter, said she feared that if Sheinbaum wins, "it will be more of the same like with Lopez Obrador, who has sunk Mexico and wants to turn it into another Venezuela."

Nearly 100 million people are registered to vote for president, members of Congress, several state governors and local officials, in the biggest-ever elections in the country of 129 million.

Security Minister Rosa Icela Rodriguez said Tuesday -- before Cabrera's murder -- that 22 people running for local office had been killed since September.

Some non-governmental organizations have reported an even higher toll, including Data Civica, which has counted at least 30 killings of candidates.

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• Mexico
• Murder
• Election