Venezuela has been plunged into uncertainty as the South American nation was urged to "pray" for Hugo Chavez amid speculation the cancer-strick president was close to death.
Public New Year's celebrations were cancelled after a rare acknowledgement of the weakening state of health of President Chavez, 58.
Nicolas Maduro, the vice-president and his heir apparent warned of a new setback following cancer surgery in Cuba and admitted that the leader faced an uphill battle.
"We were informed of new complications arising from the already known respiratory infection," Mr Maduro said late on Sunday in a sombre televised address from Havana, where he was at President Chavez's bedside.
"President Chavez's state of health continues to be delicate," Mr Maduro added, warning that the complications "are being attended to in a process that is not without its risks."
His condition has worsened following an operation on December 11 at a medical clinic in the Cuban capital – the fourth round of surgery since first being diagnosed with cancer in June 2011 – and he had reportedly suffered unexpected blood loss followed by a post-operative respiratory infection.
Authorities have been tight-lipped about the type and severity of President Chavez's cancer, except to say it affects the pelvic area. The longtime leader had in fact declared himself "totally cured" before embarking on a re-election campaign during the summer.
But the political firebrand, who has led the country since 1999 and won his third six-year term in office in October elections, was later forced to admit that he had suffered a relapse.
Venezuela seemed poised for news of its leader's demise, with rumours circulating that he had already died and the announcement deliberately delayed for political purposes.
Even Fidel Castro, a close confidante and long time ally of President Chavez and a frequent bedside visitor, appeared to bid farewell to his disciple in his latest dispatch printed in Cuba's state newspaper Granma, and to welcome his likely successor.
Addressing his letter to Mr Maduro, the 86-year-old El Commandante wrote: "The name of Hugo Chavez is admired and respected throughout the world – I have the certainty that, with him and however painful his absence, you will be capable of continuing his task."
The very real prospect that President Chavez would not be around to attend his inauguration on the constitutionally mandated date of January 10 has led to fears of fierce political upheaval in the oil-rich OPEC nation.
Senior Chavista officials have made moves to postpone the inauguration and argued that a party member could take his place without the need for new elections.
President Chavez named Mr Maduro as his successor earlier this month before travelling to Havana for the latest surgery and the vice-president has become the face of the government in his absence, taking on the President's bombastic style and issuing long anti-imperialist speeches.
But opposition figures are pushing for new elections to be called within 30 days if Mr Chavez does not return by inauguration day, as it states in the Venezuelan constitution, believing they have a good chance at winning office with the charismatic incumbent out of the running.
Commentators within Venezuela and abroad debate whether Chavismo, as his revolutionary socialist movement is known, is strong enough to survive without its undisputed leader, who has long been a thorn in America's side, blasting US influence in Latin America.
While living conditions have undoubtedly improved for Venezuela's poor during Mr Chavez's near 14 year rule, fuelled by income from high oil prices, the nation of 29 million has become one of the world's most violent and corrupt with a murder rate higher than even Colombia and Mexico.
Venezuelans were facing the start of 2013 with the promise of an uncertain transition to a post-Chavez era.
Authorities cancelled a New Year's Eve concert in a downtown plaza and Ernesto Villegas, Venezuela's minister of information, urged families "to ring in the New Year at home, praying and expressing hope for the health" of Chavez.
Twitter was awash with messages of love and support for Chavez and his family.
Mr Chavez's daughter Maria, who has been with the president since his surgery, said on Twitter: "Thank you people of Venezuela. Thank you people of the world. You and your love have always been our greatest strength! God is with us! We love you!"
Even some of his detractors were hoping for a recovery.
"I do not want Chavez to die," one Enrique Vasquez wrote. "We would look really bad as a country if a disease had to do our job of removing him from power."