Chavez waved and blew kisses to crowds while he rode atop a truck to the country's elections office, then picked up a document registering as a candidate. Afterward, he stepped onto a stage and energetically sang along with a band to a traditional tune from the rural plains where he was born. Chavez laughed and danced briefly on stage.
The 57-year-old president, a former army paratroop commander first elected in 1998, is seeking another six-year term in the Oct. 7 presidential vote. His struggle with cancer has recently forced him to scale back his public appearances and has raised questions about whether his health may interfere with the re-election campaign.
"I want to thank my Lord that I'm here today. ... It was a difficult year," Chavez said in a speech to cheering crowd. "Here I am, before you again!"
He denied rumors of worsening health, calling such speculation "psychological warfare" waged by his adversaries.
"We're just warming up our engines," he said, vowing to win the vote in a "knockout."
As Chavez registered his candidacy, he walked slowly greeting allies and elections officials. The crowd outside chanted: "Ooh-Ah! Chavez's isn't going away!"
His supporters and government employees wore their socialist party's red caps and shirts, holding photos of the president and signs reading: "We're giving it our all, out of love for Chavez." Three giant inflatable likenesses of Chavez rose above the crowd that surrounded the elections office.
Chavez wore a track suit in the yellow, blue and red of Venezuela's flag as he rode through streets lined with supporters on his way to the elections office. Confetti floated in the air as he passed. Some in the crowd waved flags, and others blew whistles and horns.
Chavez was accompanied by relatives including his brother Adan and two daughters.
Adela Blanco, who works at a government food processing company, said she thinks Chavez has been looking better lately despite his illness. "He has to rest. He has to recover in order to continue on," she said.
Chavez's rival, Henrique Capriles, led a huge crowd of supporters Sunday as he registered his candidacy, working up a sweat by marching and jogging 6 miles (10 kilometers) from a park in eastern Caracas to the headquarters of the National Electoral Council.
Climbing up on a stage in a plaza next to the elections office, Chavez spoke for more than 2 1/2 hours. He said he hopes to expand his drive to build a socialist state, and presented elections officials with what he described as a socialist plan for his government through 2019.
Chavez didn't mention Capriles by name but said his rival's speech a day earlier was bland and colorless. Chavez dismissed his opponents as "mamas' boys who never studied," and said they will be swept away in the upcoming election.
Some Venezuelan analysts have said they expect Chavez's illness could be a point against him in the presidential campaign, especially if his condition limits his strength and mobility. Despite his illness, though, Chavez's approval ratings have remained above 50 percent during the past year, and recent polls put him in the lead the over Capriles.
Elisa Bermudez, a retiree who held a sign bearing an image of Chavez, said she hopes he wins re-election in order to continue the social programs he has created. Programs offered by Chavez's government include cash benefits for poor families and neighborhood health clinics staffed by Cuban doctors.
Asked if she thinks Chavez is well enough to campaign, Bermudez said: "We'll help him."
Luis Vicente Leon, who heads the Venezuelan polling firm Datanalisis, said Chavez has managed his illness in a way that has allowed him to benefit politically so far while also avoiding having the bulk of the Venezuelan population "believe it's a deadly illness that will impede Chavez's future."
As the vote nears, though, Chavez will likely have to adjust his strategy to show he is well enough to campaign in order to avoid potential fallout, Leon said.
Chavez said Saturday that he has undergone tests following his cancer treatment and everything came out well.
The president returned from Cuba on May 11 after what he said was a difficult round of radiation therapy.
In the past year, Chavez has undergone two surgeries that removed tumors from his pelvic region, most recently in February. During Chavez's yearlong cancer struggle, he has not disclosed key details about his illness including the type of cancer or the precise location of the tumors.
Both during and after his cancer treatments, Chavez has appeared in public less frequently than he used to, a dramatic shift for a leader who for much of his 13-year-old presidency has kept a busy schedule of televised talks and rallies.
While Chavez has taken a lower profile, his government has stepped up advertising that promotes his image and programs such as public housing construction. Some of Chavez's Cabinet ministers have taken to wearing T-shirts emblazoned with a simple image showing only Chavez's eyes.
In his speech, Chavez didn't say how active he intends to be during the campaign. But he did say he soon plans to attend the inauguration of a new mausoleum to house the remains of 19th century independence hero Simon Bolivar.
His government has built a new mausoleum with a soaring, curved roof for the namesake of Chavez's Bolivarian Revolution movement. Bolivar's birthday, a national holiday, is coming up on July 24.