CARACAS -- In an impressive show of force that closed down much of the capital and overflowed the central plaza with supporters, Venezuelan presidential candidate Henrique Capriles, 39, registered his candidacy on Sunday.

As hundreds of thousands of people congregated in downtown Caracas, Capriles vowed to unseat President Hugo Chávez on Oct. 7 and unite a nation that has become increasingly polarized.

“There are not two Venezuelas, there is only one,” Capriles told cheering crowds before he registered with the National Election Council. “Power shouldn’t be used to divide but unite.”

On Monday, Chávez will get to measure his political strength, vowing to flood the city with “a sea” of followers when he registers his candidacy. The event will also give the president an opportunity to dispel rumors and showcase his recovery from an undisclosed form of cancer that has hounded him for almost a year.

Capriles was the governor of Miranda State, part of greater Caracas, until Wednesday, when he turned the position over as required by law. During his four years in the gubernatorial office, he won praise for being an energetic and dedicated leader who would say he was always too busy to have a wife or family. He has also won high marks for reaching across the political divide to work with Chávez supporters.

Capriles, who is still running behind in most polls, has tried to assure disgruntled Chávez backers that they have a different option.

“I’m not the enemy of anyone,” Capriles said. “I am an enemy of problems. I’m an enemy of violence. I’m an enemy of a country that has everything it needs to get ahead but has a government that won’t let it.”

His conciliatory tone has helped win him support from unlikely sectors.

Flying above the crowd Sunday were the flags of Bandera Roja and Vanguardia Popular, leftist political parties that have lost faith in Chávez.

“Chávez was the great hope for our cause, but we’ve given up on him because he has turned his back on the people even as he claims to be the voice of the people,” said Dick Guanique, 56, the secretary general of Bandera Roja, or Red Flag, a communist party. “It’s not that we’re enthusiastic about Capriles, but we think he’s the only way out of a regime that’s become authoritarian.”

In February, a coalition of opposition parties that united to end Chávez’s 13-year presidential run held their first primary in February. Capriles won that race by almost a million-vote margin, and his five primary rivals have become some of his biggest cheerleaders.

“Today, we’re seeing the fruits of our decision to unite behind the person who will be the president of all Venezuelans,” said Leopoldo López, the former mayor of Chacao, who had been one of Capriles’ chief competitors early in the race.

On Sunday, Chávez said that he would use his candidacy registration to present a national plan for his next six years in office. Monday is a bank holiday, and Chávez invited followers from all over the country to crowd into the city.

“From what I’m told, Caracas is going to overflow,” Chávez said on TV. “I don’t know where we’re going to fit all the people.”