President Hugo Chavez's new complications after cancer surgery have prompted his closest allies to call for Venezuelans to pray for him.
The reports fuelled renewed speculation about whether the ailing leader has much longer to live.
Vice President Nicolas Maduro looked weary and spoke with a solemn expression as he announced in a televised address from Havana on Sunday that Mr Chavez was facing "new complications" due to a respiratory infection nearly three weeks after his operation.
He described Mr Chavez's condition as "delicate".
The streets of Caracas were abuzz yesterday with talk of Mr Chavez's increasingly tough fight, while the news dominated the front pages of the country's newspapers.
A planned New Year's Eve in Caracas concert was cancelled due to Mr Chavez's condition.
The president's aide prayed at a televised Mass held at the presidential palace, while his allies urged Venezuelans to keep their president in their prayers.
Political analyst Ricardo Sucre said Mr Maduro's body language during his televised appearance spoke volumes.
"Everything suggests Chavez's health situation hasn't evolved as hoped," Mr Sucre said.
He said Mr Maduro was probably staying in Havana to keep close watch on how Mr Chavez's condition develops.
"These hours should be key to having a more definitive prognosis of Chavez's health, and as a consequence make the corresponding political decisions according to the constitution," he added.
Mr Sucre said it seems increasingly unlikely that Chavez would be able to be sworn in as scheduled on January 10.
The Venezuelan leader has not been seen since undergoing his fourth cancer-related surgery on December 11, and government officials have said he might not return in time for his inauguration.
If Mr Chavez dies or is unable to continue in office, the Venezuelan Constitution says that a new election should be held within 30 days.
Before his operation, Mr Chavez acknowledged he faced risks and designated Mr Maduro as his successor.
Mr Chavez has been fighting an undisclosed type of pelvic cancer since June 2011.
Mr Maduro said on Sunday that he had met with Mr Chavez. "We greeted each other and he himself referred to these complications," Mr Maduro said, reading from a prepared statement.
"The president gave us precise instructions so that, after finishing the visit, we would tell the (Venezuelan) people about his current health condition," Mr Maduro said. "President Chavez's state of health continues to be delicate, with complications that are being attended to, in a process not without risks."