Mexico's cartels cast an ugly shadow over Sunday's elections, the heavy police and military presence doing little to quell the fears of anxious voters in areas worst affected by the country's rampant drug violence.
More than 50,000 people have been killed since President Felipe Calderon in late 2006 deployed Mexico's military to crush the well-armed cartels that make their wealth mainly by smuggling drugs -- especially cocaine from South America -- into the United States.
Soldiers and marines patrolled violent regions like the eastern states of Veracruz, Tamaulipas and Nuevo Leon, where the Sinaloa syndicate of Joaquin "Chapo" (Shorty) Guzman has been battling the ultra-violent Zetas cartel for control of smuggling routes and crime rackets.
In the port of Veracruz, marines in ski masks armed with automatic rifles protected voting stations. A shoot-out near one booth in the Ozuluama neighborhood left two people dead, terrified election workers and delayed the start of voting.
"People are scared," poll worker Antonio Manjarrez told AFP as he re-opened the station with help from voters standing in line.
Several Veracruz state candidates have received death threats in recent weeks. On Thursday, the body of a town mayor who had been kidnapped was found dead, wrapped up in election posters. She wasn't even running for office.
Extra army patrols were deployed in the northern border town of Nuevo Laredo, where a car bomb -- a rarity in Mexico -- was detonated on Friday in front of the mayor's office, injuring some pedestrians.
"With everything that has gone on in the last days we prefer to come early to vote," a fearful Carmen Gonzalez told AFP as she headed to the polls in Nuevo Laredo. "Then we'll gather with our family. It's not safe to be walking around outside."
The governor of the central state of Guanajuato, Hector Lopez, asked for federal security reinforcements after a vote monitor from a leftist party was murdered on Saturday.
In the southern state of Guerrero, a mayoral candidate for the Institutional Revolutionary Party (PRI), which looks set to sweep back to power with Enrique Pena Nieto at the helm, was found near a highway beaten by assailants.
Early turnout was heavy in the dangerous northeastern state of Nuevo Leon. "We have military patrols all over the place," Jorge Domene, a spokesman for the state governor, told AFP.
Security "is the most important issue, that's what determined my vote. But I won't say who I voted for," Gabriel Gonzalez, 49, told AFP in the industrial city of Monterrey.
Gonzalez was speaking outside a police station that had been close months earlier when assailants opened fire and hurled a grenade at the building.
"If we don't start with safety, we can't have anything," Nidia Garza, 30, told AFP in the nearby town of Apodaca.
President Calderon was monitoring events from Mexico City.
"There have been some incidents, but they are isolated," he said after voting and following a meeting with his security council.
Opinion polls predicted a clear victory in the presidential race for Pena Nieto of the center-left PRI, which governed Mexico for more than seven decades until 2000.