Pope John Paul II's condition remains very serious and he has started to show signs of losing consciousness, the Vatican's official spokesman has said.
The Pope asked not to return to hospital for treatment
But at a briefing on Saturday morning, Joaquin Navarro-Valls insisted the 84-year-old, who has heart and kidney problems, was not in a coma.
Crowds have formed again on St Peter's Square after last night's vigil.
The Vatican spokesman said Mass had been celebrated in the presence of the pontiff during the morning.
"Sometimes it seems as if he were resting with his eyes closed, but when you speak to him, he opens his eyes," he told reporters.
However, Mr Navarro-Valls stressed the gravity of the Church leader's condition, noting his "general cardio-respiratory and metabolic conditions" were "substantially unvaried and therefore very grave".
"Since dawn this morning there have been first signs that consciousness is being affected," he said.
'About to die'
Newspapers in Italy and across the world splashed farewell messages to the Pope on Saturday.
Prayers have been offered up for the pontiff worldwide
"Long Farewell to the Dying Pope" read a headline in La Repubblica while Il Tempo simply said "Ciao, Karol", using the Polish-born Pope's original first name.
All Italian sports competitions, including Serie A football matches, were suspended on Saturday out of respect for the pontiff, the Italian Olympic Committee said.
Cardinal Javier Lozano Barragan, head of the Vatican's health care office, meanwhile told Mexican TV the Pope was "about to die".
"I talked to the doctors and they told me there is no more hope," the Mexican cardinal said.
Lights burned through the night in the Pope's window as several hundred people, many of them tearful, stayed out in the square, wrapped in blankets to shield them from the cold.
Sister Arlete, a nun who attended morning Mass at the Vatican, said that while she felt sadness at the Pope's approaching death there was " happiness that his suffering will end because he's truly suffering".
Heading for Rome
Having refused to return to the Gemelli hospital where he was treated last month for breathing difficulties, the Pope is being treated in his Vatican apartment by a team of four top consultants and his private doctor, Renato Buzzonetti.
His condition had deteriorated on Thursday after he developed a urinary tract infection that later brought on "septic shock and a cardio-circulatory collapse", and he received the last rites.
Cardinals in the United States and Latin America have indicated they are preparing to travel to Rome.
John Paul II's eventual successor will be elected in a secret vote at the Vatican's famed Sistine Chapel by the cardinals - the "princes" of the Christian world's largest Church.
Prayers for the Pope have also been offered by other religions: Jews in Jerusalem and Muslims in Indonesia.
The Communist authorities in Cuba allowed the Church leader there, Cardinal Jaime Ortega, to make a rare statement on television.
"A great man is dying," he said in the six-minute address. "This is a man who has carried the moral weight of the world for 26 years... turning himself into the only moral reference for humanity in recent years of wars and difficulties."
Many view the undermining of Communism in Roman Catholic countries of Eastern Europe as one of the Polish pontiff's main achievements.