Thousands of Chavez supporters fervently swore "absolute loyalty" on Thursday to the charismatic Chavez, who has held a vice-like grip over the country's politics for 14 years and is currently recovering from his fourth surgery in Cuba.

The opposition meanwhile called for counter-demonstrations on January 23, the day in 1958 that began Venezuela's modern democratic era with the ouster of its last military dictatorship.

Leopoldo Lopez, an opposition leader, said Chavez's failure to turn up to his own ceremony had created "an undefined situation in which we can be without a president, and without clear signs that the president is governing."

The Supreme Court has ruled the cancer-stricken Chavez can postpone his swearing-in indefinitely, and the government has not given an indication of when the president might return.

Many regional leaders have stood with Chavez, including several who turned up at the rally.

And Argentina President Cristina Kirchner on Friday was headed to Cuba, where the Venezuelan leader is recovering from his fourth surgery, to get a better picture of his condition, her office announced on the government website.

Her foreign minister, Hector Timerman, had represented Argentina at the rally in Caracas.

But it was the pro-Chavez masses who dominated the day, pouring out of buses from the early morning to rally behind the government in a celebration that was by turns festive and fervent.

A sea of red shirts and flags, the color of Chavez's socialist movement, filled the avenue in front of the Miraflores presidential palace where participants took a symbolic oath for the 58-year-old.

"Comandante, get better, because this people has sworn and is going to show absolute loyalty. So we have sworn. Long live Chavez!" Vice President Nicolas Maduro said as he led the oath.

Maduro's speech lavished praise on Chavez and his socialist revolution and accused the opposition of harboring desires for a coup.

He urged the police to closely watch what the opposition does, accusing them of "looking to stain this special moment in this life of our peoples."

Russian-made Sukhoi fighter jets streaked the length of this mountain valley and the crowd delivered a booming rendition of the national anthem and roared with approval for the tributes from leftist leaders like Bolivia's Evo Morales, Uruguay's Jose Mujica and ousted Paraguayan leader Fernando Lugo.

"There is a man who is fighting for his life, who is in your hearts," said Mujica. "But if tomorrow, he is no longer -- unity, peace and work."

It was the day's most direct reference to the possibility that Chavez, who has been in a Cuban hospital and out of public view for a full month, may die.

Bands played patriotic anthems from stages erected along the streets.

Shouts of "Chavez, Chavez!" and the anti-opposition chant "They will not return" could be heard as Chavista militants stoked the crowds with fiery speeches.

Faithful flocked to one stage for an evangelical religious service, while street vendors sold Chavez memorabilia on the sidewalk.

"I love the president," said Pedro Brito, a 60-year-old law professor, in a red T-shirt with the slogan "I am Chavez."

"He has done a lot for poor people, the ones who had no place to sleep or food to eat. He has shown us how to love the country."

Gladys Guerrero, 35, said she traveled by bus from the eastern state of Monagas "to repay love with love."

The Supreme Court upheld a decision to indefinitely postpone Chavez's swearing-in ceremony and said his existing administration could remain in office until he is well enough to take the oath.

It was the last legal hurdle to a government plan for resolving the vacuum created by Chavez's illness that met fierce resistance from the opposition, which had argued it was unconstitutional.

Henrique Capriles, who ran unsuccessfully against Chavez in October presidential elections, accepted the Supreme Court ruling as "binding" but said it did not end the uncertainties facing the oil-rich country.

The military announced it was reinforcing security in Caracas and at other strategic points to ensure the day was observed peacefully.

And the government stopped a broadcaster, Globovision, from airing videos about the controversy over Chavez's non-inauguration, saying they risked inciting political "intolerance."

Globovision, known for being critical of the government, denounced the ban as an act of censorship.

The government has said that Chavez is recovering from complications from surgery, most recently a severe pulmonary infection that had resulted in a "respiratory insufficiency."

Information Minister Ernesto Villegas said late Monday that Chavez's medical condition was unchanged.

Supreme Court president Luisa Estella Morales, who read out the decision upholding the inauguration delay, also ruled out convening a medical board to assess the health of the president.

Throughout his illness, first detected in June 2011, Chavez has refused to relinquish the powers of the presidency, even when leaving for Cuba for his latest surgery.

The charter says new elections must be held within 30 days if the president-elect or president dies or is permanently incapacitated, either before he takes office or in the first four years of his six-year term.