Italian news agency ADNKronos, without citing sources, reported that a brain monitor hooked to the Pope had gone flat. But a senior Vatican official said the Pope was still alive and that there was no such monitoring device in his apartment.
Another agency, APCom, said the Pope's situation was critical but also said John Paul II was not connected to a monitor.
The Ansa news agency said there was no brain monitor in the Pope's third-floor apartment overlooking St Peter's Square. The monitor that had been mentioned was known as an electroencephalogram, or EEG, which measures brain wave activity.
The Vatican said on Friday morning that John Paul II had suffered blood poisoning from a urinary tract infection on Thursday and later reported his condition had deteriorated.
"The general conditions and cardio-respiratory conditions of the Holy Father have further worsened," the Vatican said in a statement issued at 6.30pm (1630 GMT).
"The clinical picture indicates cardiocirculatory and renal insufficiency," it said. "A gradual worsening of arterial hypotension has been noted and breathing has become shallow."
"The Holy Father - with visible participation - is joining in the continual prayers of those assisting him," said the communique issued by papal spokesman Joaquin Navarro-Valls.
Pope reported unconscious
Italy's APCom news agency, without citing sources, reported late on Friday that the Pope was unconscious. Vatican officials were not immediately available for comment.
Earlier, the Vatican had denied another report by the same agency that claimed the pontiff had slipped into a coma.
St Peter's Square remains
crowded with the faithful
RAI television reported that the Bronze Door beneath a portico off St Peter's Square - which is traditionally shut when a Pope dies - had one of its massive doors closed as about 30 police officers stood nearby.
The door normally is closed every night at 8pm and reopened the next morning, and it was unclear what, if anything, a half-shut portal would signify.
Earlier on Friday, the Vatican said the 84-year-old Pope was still lucid, fully conscious and "extraordinarily serene".
Navarro-Valls, breaking into tears at times, said in the earlier briefing that John Paul II was "informed of the gravity of his situation" and decided to remain in his apartment overlooking St Peter's Square, where thousands of people stood vigil.
They stared up at the window from where the first Polish Pope has addressed millions of faithful during an extraordinary 26-year papacy, the third longest in Church history. He was last seen there two days ago, gaunt and unable to speak.
"The Pope's faith is so strong and full and the experience of God so intensively lived that he, in these hours of suffrance ... already sees and already touches Christ," Cardinal Camillo Ruini, the Pope's vicar for Rome, told hundreds who crowded a Rome basilica on Friday evening for a special Mass for the Pope.
'Very grave' condition
Navarro-Valls said that after John Paul II's already fragile health declined sharply on Thursday evening, he participated in Mass from his bed and received seven top aides on Friday morning.
"The Pope is still lucid, fully conscious and extraordinarily serene," Navarro-Valls said. But he said he remained in a very grave condition with unstable blood pressure.
The Pope at the Vatican City in
January this year
John Paul II asked aides to read him the biblical passage describing the 14 stations of the Way of the Cross, the path that Christ took to his crucifixion and burial, Navarro-Valls said. The Pope followed attentively and made the sign of the cross, he said.
John Paul II also asked that scripture of the so-called Third Hour be read to him. The passage is significant because, according to tradition, Christ died at three o'clock in the afternoon.
"This is surely an image I have never seen in these 26 years," the usually unflappable Navarro-Valls said.
Choking up, he walked out of the room.
Later, the Vatican said the Pope appointed a large number of bishops and other church officials.
Cardinal Marcio Francesco Pompedda, a high-ranking Vatican administrator, visited him on Friday and said he opened his eyes and smiled.
"I understood he recognised me. It was a wonderful smile - I'll remember it forever. It was a benevolent smile - a father-like smile," Pompedda told RAI television. "I also noticed that he wanted to tell me something but he could not... But what impressed me very much was his expression of serenity."
John Paul II's medical problems have been building over the past decade, since he first showed the symptoms of Parkinson's disease, a progressive neurological disorder.
He was hospitalised twice last month because of breathing problems and had a tube inserted in his throat.
On Thursday, he suffered a cardio-circulatory collapse and septic shock during treatment for a urinary tract infection, the Vatican said.
He received the sacrament for the sick and dying on Thursday evening. Formerly called the last rites, the sacrament is often misunderstood as signaling imminent death. It is performed both for patients at the point of death and for those who are very sick - and it may be repeated.
The Rome daily La Repubblica reported on Friday that the sacrament was administered by John Paul II's closest aide, Polish Archbishop Stanislaw Dziwisz, who serves as his private secretary. Dziwisz had given the pontiff the same sacrament on 24 February just before the Pope underwent a
tracheotomy to insert a breathing tube in his throat at the Gemelli Polyclinic hospital, the newspaper said.
Vatican medical team
Former Detroit Archbishop Edmund Szoka, of Polish extraction and one of the Vatican officials to visit the papal apartment on Friday, said John Paul II was "having trouble breathing, and that's the difficulty".
"He has a very strong heart," Szoka told Detroit's WXYZ-TV. "If he can get his breathing back, if they can do something to get him to breathe again normally, he could be all right, he could get well."
John Paul II was attended to in his apartment by the Vatican medical team and provided with "all the appropriate therapeutic provisions and cardio-respiratory assistance," the Holy See said.
The Roman Catholic community
is waiting for news
It said the Pope was being helped by his personal doctor, two intensive care doctors, a cardiologist, an ear, nose and throat specialist and two nurses.
Heart failure occurs when the heart no longer has the strength to pump blood through the body, and is a sign that the body's cardiac system is failing.
Dr Peter Weissberg, medical director of the British Heart Foundation, said septic shock "puts a phenomenal strain on the heart".
"The chances of an elderly person in this condition with septic shock surviving 24 to 48 hours are slim - about 10 to 20%, but that would be in an intensive care unit with very aggressive treatment," said Dr Gianni Angelini, a professor of cardiac surgery at Bristol University in England.
Hospitalised twice last month after two breathing crises, and fitted with a breathing tube and a feeding tube, John Paul II has become a picture of suffering.
His 26-year papacy has been marked by its call to value the aged and to respect the sick, subjects the Pope has turned to as he battles Parkinson's disease and crippling knee and hip ailments.
It is not clear who would be empowered to make medical decisions for an unconscious Pope.
The Vatican has officially declined to comment on whether John Paul II has left written instructions, but Vatican experts say Dziwisz, the Pope's longtime secretary, would be expected to have a say.