Thousands of protesters caused commuter chaos by closing off Mexico City's business district to traffic on Monday, pressing the main leftist candidate's demand for a vote recount in a presidential election he says was stolen from him.
Launching a campaign of civil disobedience that raises the stakes in Mexico's political crisis, Andres Manuel Lopez Obrador's supporters seized control of the capital's imposing Zocalo square on Sunday night as well as a six-mile (10-km) stretch of the elegant Reforma boulevard.
They set up tents and huge tarpaulin covers in the middle of the wide, tree-lined avenue, cutting off all commuter traffic on Monday morning. The avenue is home to Mexico's stock market, many luxury hotels, government offices, headquarters of major corporations and the US embassy.
The several thousand demonstrators did not close down buildings so workers were allowed into their offices, but the occupation caused long delays for many commuters. Some were furious.
"I had to cancel a breakfast where I was going to close a contract for one million pesos (about $92,000). Do you think I'm happy, or that I support these bastards?" said Enrique Salas, an insurance broker who was one of thousands forced to walk to work along Reforma. The Mexican peso fell 0.52 percent to 10.9160 to the dollar on Monday morning as investors became nervous about the protests.
Lopez Obrador apologised to those who do not back his cause but said his campaign to overturn the July 2 election that he narrowly lost to conservative ruling party candidate Felipe Calderon would save Mexico's young democracy.
"I hope that some day they will understand us, understand that this struggle is necessary, not just for us but for everyone," he told hundreds of thousands of supporters at the end of a huge protest march through the capital on Sunday.
Local police could break up the protests but that is unlikely as the city and its police force are run by Lopez Obrador's Party of the Democratic Revolution. He was mayor until he stepped down last year to run for president.
"They wanted to steal the elections from us but we are not giving in," said Magdalena Salazar, a middle-aged woman who backs Lopez Obrador and danced with her daughter in the Zocalo as a salsa band played into the early hours of Monday.
"If they don't pay attention to us, we'll shut the city down," she said. Hundreds slept on the ground and Lopez Obrador also stayed in the Zocalo all night, although he went home for a shower early on Monday.
Calderon's margin of victory was just 244,000 votes, or less than 0.6 percentage points, and Lopez Obrador says results from more than half of polling stations were tampered with.
The battle is now with Mexico's highest electoral court and Lopez Obrador is trying to push it into ordering a full recount, while Calderon insists there was no fraud.
The seven judges have to decide whether to reopen some or all of the ballot boxes by August 31. That means Lopez Obrador's occupation of the capital could last for weeks.