MEXICO CITY: A man lobbed a severed human head at a voting station in the border city of Tijuana on Sunday and plastic bags filled with body parts were found nearby, local authorities said, as Mexicans voted across the country in midterm elections.

Authorities said the man ran away, but they did not specify whether he was captured. They said they found plastic bags with human remains and severed hands in the area.

It was not immediately clear what message the gruesome act was meant to send and how it related to Sunday's election.

The campaign for lawmakers and state authorities has been one of the bloodiest in Mexico's recent history. Security consultancy Etellekt said 97 politicians had been killed and 935 were attacked.

Elsewhere on voting day, someone threw an inactive grenade into a voting station in Mexico State, authorities said. One voter, who asked not to be named, told Reuters that the crowd dispersed but then returned.

"People said that they would vote, and that they would not be intimidated," the person said, adding that she had cast her ballot. "It was ugly."

In Sinaloa, armed men robbed electoral material from voting stations, a source at the state prosecutor's office said.

All 500 seats in the lower house of the federal Congress, 15 state governorships and thousands of local leadership positions are up for grabs, with 93.5 million Mexicans eligible to vote.

Erik Ulises Ramirez, a candidate for the left-wing opposition Citizen's Movement party who survived an assassination attempt last month in Cocula, Guerrero state, said two of his allies ad been kidnapped, beaten and then released on Sunday.

Security analysts said most electoral violence tends to occur at the municipal level, where gangs exert pressure to influence the outcome in the hope of securing more control over drug trafficking and other criminal rackets.