Peña Nieto takes lead in Mexico presidential poll

• Four candidates are vying for Mexico's presidency
• Voters cast ballots for federal, state and local offices
• Authorities call it the "largest and most complex election day" in Mexico's history

Follow the Mexican election coverage in Spanish at CNNMéxico.com

Mexico City (CNN) -- Mexicans headed to the polls to vote Sunday in what officials have called "the largest and most complex election day" in the country's history.

Four candidates are vying for the presidency. Voters will also cast ballots in congressional contests and, in six states, gubernatorial races.

"Never in Mexican democracy have so many posts been at play in the same popular election," Federal Election Institute President Leonardo Valdes said in a statement.

More than 2,100 federal, state and local offices will be decided by Sunday's vote, the institute said.

For the first time, more than 79 million people were registered to vote, according to the institute. Among them are 3.5 million young people who will vote for the first time, the institute said.

Nationwide, authorities said there would be more than 143,000 polling stations and more than 13,000 accredited observers.

Mexicans also cast ballots from beyond the country's borders. On Saturday, election officials they had received 40,737 absentee ballots from Mexicans living abroad.

Voters will elect new governors in the states of Chiapas, Guanajuato, Jalisco, Morelos, Tabasco and Yucatan. In Mexico City, the nation's capital, residents will elect a new mayor.

CNN's Krupskaia Alis and Rene Hernandez and CNNMexico.com contributed to this report.