"He's battling for his life, for his health, and we are there with him," Nicolas Maduro said in nationally televised remarks at a ceremony at a parish house in Caracas, the capital.
"Our commander is sick because he gave his life for those who don't have anything," Maduro said in a ceremony giving government housing to people in a slum who lost their homes in 2010 torrential rains.
The 58-year-old Chavez -- reported by the government to be in a downtown Caracas military hospital since Feb. 18 after being treated in Havana for complications following Dec. 11 cancer surgery in Cuba -- spent many sleepless hours thinking of how to improve housing, services and the quality of life for Venezuelans but forgot about his own health, Maduro said.
"He completely surrendered body and soul and forgot all his obligations to himself in order to give himself to the homeland," Maduro said.
Maduro, 50, a former bus driver and Chavez's self-appointed successor, asked those receiving the housing to remain loyal "to the man who has given everything" for their country.
Chavez hasn't been seen publicly since flying to Havana Dec. 10.
Maduro's remarks were the second time in two days he spoke about Chavez giving his life for his people.
He made similar remarks the day before at the end of a ceremony commemorating the 24th anniversary of a popular uprising against the government of Carlos Andres Perez, sparked by increases in gasoline prices.
Chavez famously said the "Caracazo" riots in Caracas and surrounding towns -- which the government said left 340 people dead but rights groups say killed more than 1,000 -- sowed the seeds for his coming to power a decade later.
In his remarks Thursday, Maduro called opposition leaders demanding proof Chavez is alive "traitors [who] will never believe in anything."
His challenge came amid reports Chavez had died.
Guillermo Cochez, until recently Panama's ambassador to the Organization of American States, told newspaper La Estrella de Panama Wednesday his sources at senior levels in Venezuela's government told him Chavez was dead after being taken off life support about four days earlier at his daughters' orders.
"If I lie, let the government of Venezuela simply show Chavez to everyone," Cochez said, adding Chavez was in a vegetative state since the end of December.
Cochez, who was dismissed from his post Jan. 17 after criticizing the OAS for failing to be tougher on Venezuela, also said the four photographs Caracas released Feb. 15 of Chavez lying in a bed in Cuba with his two daughters by his side appear to have been taken some time ago, rather than Feb. 14, as the government says.
He said one of Chavez's daughters had rhinoplasty, or plastic surgery of the nose, last year, but the photos appear to show her with her old nose.