Caracas, Venezuela (CNN) -- Venezuelan President Hugo Chavez filed the formal paperwork declaring his re-election bid Monday, as cheering crowds packed a plaza outside the election authority headquarters in Venezuela's capital.
Wearing his trademark red beret, Chavez rode into the crowds atop a truck. He smiled broadly and blew kisses.
State-run VTV showed Chavez supporters wearing red shirts, cheering as they waved banners and flags.
Since Chavez first announced his cancer diagnosis nearly a year ago, speculation has surged over the 57-year-old Venezuelan leader's health and political future.
But the president and his supporters have maintained that his battle against cancer has only strengthened his resolve to win the October 7 presidential vote.
Opposition candidate Henrique Capriles Radonski registered on Sunday.
Wearing a Venezuelan national soccer jersey, he spoke to throngs of supporters.
"Let us never forget this day. Today we all came to sign a pledge. And our pledge is named Venezuela," said Capriles.
At his formal registration, the 39-year-old the governor of the Venezuelan state of Miranda sported a shirt with the yellow, blue and red stripes of the country's flag.
Monday was Venezuela's deadline for securing a spot on the ballot.
But both Chavez and Capriles have been promoting their presidential bids for months.
Capriles, who has also served as a mayor and a congressman, cruised to a win in February's opposition coalition primary, casting himself as a center-left candidate seeking to appeal to voters across the political spectrum.
Chavez's cancer has forced Capriles to walk a tightrope in his campaign.
"We don't wish ill to anyone," Capriles told CNN en Español last month, saying he wants Chavez's tenure to come to an end at the ballot box.
"I think a government for too long is a bad thing," he said. Chavez leads "a government that is more concerned with trying to convince Venezuelans that the problems don't exist, instead of solving them."
Chavez has led Venezuela since 1999 and repeatedly pledged to run for re-election in October.
The outspoken, flamboyant socialist leader has not specified the type of cancer he is fighting, and the government has released few specifics.
Last week he said he was putting the finishing touches on the campaign platform that is required to register to run, the state-run AVN news agency reported.
"We are not starting from zero. We have a plan for the country. The national project goes beyond a simple plan. It is part of the long-term vision that we have already been building, and will extend into the future," Chavez said, according to AVN.
Journalists Osmary Hernandez and Fernando Ramos contributed to this report.