(CNN) -- Health problems prevented Venezuelan President Hugo Chavez from coming to Caracas for an inauguration ceremony Thursday, but throngs of supporters swore an oath of loyalty in his absence.
Thousands of red-clad Chavez supporters packed the streets around the presidential palace for a symbolic swearing-in for the president's fourth term.
Chavez, 58, is undergoing cancer treatment in Cuba and has not made a public appearance since doctors operated on him a month ago.
On Thursday, Vice President Nicolas Maduro called on the masses gathered to take an oath of "absolute loyalty to the leadership of Comandante Hugo Chavez."
"I swear by the Bolivarian constitution that I will defend the presidency of Comandante Chavez in the street with reason, with truth and with the strength and intelligence of a people who have been liberated from the yoke of the bourgeoisie," Maduro said.
The crowd repeated his words, holding thousands of tiny copies of the constitution up in the air.
Many waved flags and carried photos of the ailing president.
Before he left for Cuba for surgery last month, Chavez said he wanted Maduro to assume the presidency if he becomes incapacitated and called on voters to support him at the polls.
Thursday's rally came as authorities continue to reassure Venezuelans that Chavez's government remains unified and intact just days after announcing that Chavez wasn't well enough to be sworn in on Thursday, specified by the constitution as inauguration day.
The country's Supreme Court on Wednesday handed a victory to Chavez's party, which had argued that the president did not need to be present at his swearing-in for his next term to begin.
But several key questions remain: How long will Chavez be in Cuba for cancer treatment? How dire is his medical situation? And will simmering political tension about who's running the country boil over?
Maduro didn't provide specifics about Chavez's health condition Thursday but said he was still "in battle."
"From here we say, 'Comandante, don't worry, continue your battle. Here there is a Bolivarian government and a revolutionary people supporting you,'" Maduro said.
In the rally, which lasted for hours and was broadcast on national television, thousands of Chavez supporters waved signs, chanted and sang. State television showed one supporter toting a handmade sign with a picture of Chavez next to a painting of Jesus.
"We came to support our president," said Marbelys Pena, a resident of Venezuela's Bolivar state who came to Caracas for Thursday's rally. "We really need him and we want him to get better."
Speaking from behind a podium that said "We are all Chavez," Latin American leaders and close allies of Venezuela pumped up the crowd with speeches praising the president and his political ideology.
"The issue of the health of brother Chavez is a problem and a worry not just of Venezuela, but of all the anti-imperialist, anti-capitalist people," Bolivian President Evo Morales said.
"Soon, soon, he will return to lead this revolution," Morales said, drawing cheers from the crowd.
Uruguayan President Jose Mujica offered more somber words of encouragement.
"There is a man who is battling for his life, and he is in your hearts. ... But if he is not here tomorrow, unity, peace, and work," he said.
Nicaraguan President Daniel Ortega described political opponents of Chavez as "vultures" who were hoping for the Venezuelan president's death and aiming to destabilize the country -- an accusation many speakers made at Thursday's rally.
Opposition politicians have argued that delaying Chavez's swearing-in without designating a temporary replacement leaves no legitimate leader in charge of Venezuela.
Chavez allies, including a majority of lawmakers in the country's congress, have said he should remain in power while taking the time he needs to recuperate.
Venezuela's Supreme Court backed the government's position, ruling that Chavez begins a new term on Thursday and can be sworn in later before the court.
Last week, a government spokesman said Chavez was battling a severe lung infection that has caused respiratory failure.
His condition remained unchanged, the government said in a statement Monday.
"Treatment has been administered permanently and rigorously, and the patient is supporting it," the statement said.
While reports from CNN affiliate Globovision included discussions of political uncertainty Wednesday, state television broadcasts showed presidents and foreign ministers arriving in Venezuela, walking on a red carpet at the airport as soldiers stood guard.
Meanwhile, Venezuelan opposition leaders called on officials from other countries to cancel their plans to attend.
Henrique Capriles, who lost to Chavez in October's presidential election, said he had reached out to foreign ministries to ask them not to send representatives.
"They are trying to put presidents from the Americas in a political rally," he said.
CNN's Mariano Castillo, Paula Newton and Rafael Romo and journalist Osmary Hernandez contributed to this report.