Tens of thousands of supporters of leftist presidential candidate Andres Manuel Lopez Obrador headed to Mexico City on Wednesday, leaving mountain towns and sprawling industrial cities to demand a ballot-by-ballot recount.

Protesters were gathering outside each of the country's 300 electoral districts before heading to the capital, where a mass rally is planned for Sunday to denounce official results showing conservative Felipe Calderon as the apparent winner of the July 2 election.

Supporters of Andres Manuel Lopez Obrador, presidential candidate of the Party of the Democratic Revolution (PRD), protest in demand for a full recount of all the ballots from the general election held ten days ago, after the federal electoral institute announced that he had lost his presidential bid by just over 200,000 votes, in Mexico City July 12, 2006. The poster on the right reads 'Vote by vote, polling station by polling station, AMLO President' in Spanish. REUTERS/Tomas Bravo (MEXICO)

Lopez Obrador aide Jesus Ortega said late Wednesday that more than 40,000 people had begun their journey and promised that Sunday's demonstration would be "gigantic."

In the candidate's home state of Tabasco, dozens of supporters wearing yellow — the color of Lopez Obrador's Democratic Revolution Party — and carrying signs that read "Vote by vote! No to electoral fraud!" began a 60-mile protest march.

Many of those marching joined Lopez Obrador in 1995 during months of protesting his loss of the governor's race in Tabasco state, organizers said.

Most marchers walked along sidewalks to avoid blocking traffic. Some chanted "Obrador, our friend, the people are with you!" as they walked along a highway leading to the Gulf coast state of Veracruz, where they planned to board busses to take them the last 373 miles of their journey to Mexico City.

About 100 people marched to Mexico City's main plaza, the planned site for Sunday's rally.

"This is a peaceful movement, but we're going to keep it up until we achieve our goal," said Mexico City homemaker Yolanda Hernandez, 34. "We are poor people who support Lopez Obrador's platform."

In the coastal states of Veracruz and Guerrero, Lopez Obrador's supporters demonstrated outside the electoral offices and then joined caravans heading to Mexico City.

Lopez Obrador has repeated promises that the protests will be peaceful, although one of his top advisers said Wednesday people could get restless.

"There is no problem of ungovernability right now, but as more time passes, there will be," Manuel Camacho Solis told reporters.

Lopez Obrador has filed legal appeals challenging the official tally of the more than 41 million votes cast. He claims the results were marred by fraud and a dirty campaign. His party has submitted dozens of boxes stuffed with videos, campaign propaganda and other alleged proof of election misconduct.

President Vicente Fox has denied interfering in the election, and monitors from the European Union said they found no irregularities in the count, which gave Calderon of Fox's ruling National Action Party a 244,000-vote advantage after an official tally.

The country's electoral tribunal in the coming days will begin weighing hundreds of appeals regarding alleged vote fraud.

"If the electoral tribunal disappoints us, I believe there is going to be a big problem," said Luis Herrera, 30, who marched with about 100 others Lopez Obrador supporters in one protest held in Mexico City.

Throughout his political career, Lopez Obrador has used street protests to pressure the government and the courts.

Last year, as Mexico City mayor, he led huge street protests that eventually forced Fox's administration to drop a legal case that would have kept Lopez Obrador out of the presidential race.

On Saturday, more than 100,000 of his supporters gathered in Mexico City's central plaza to hear his allegations of fraud.

Lopez Obrador promised to govern for the poor and forgotten, with plans for government handout programs and public works projects. Many supporters were devastated by his apparent loss, and have said they won't accept it.

The law allows a recount only for specific polling places where credible evidence of irregularities exist. The leftist's supporters say that applies to at least 50,000 of the approximately 130,000 polling places.

Lopez Obrador has also argued that there were campaign violations even before the vote, including overspending by Calderon's National Action Party, government support for Calderon and unfair intervention on his rival's behalf by business and church groups.

Under Mexican law, no president-elect will be declared until the appeals process is completed. The widely respected tribunal has overturned two gubernatorial races in recent years, both for meddling by the ruling party.

A winner must be declared before Sept. 6.

Copyright © 2006 The Associated Press

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