The Vatican said the 84-year-old Pontiff had difficulty breathing and his blood pressure had dropped to dangerously low levels.
But it denied Italian media reports that the Pope, who received the blessing for the dying after his health deteriorated late on Thursday, had died.
Sky Italia TV, quoting a report from Italy’s Apcom news agency, said the Polish-born Pope had lost consciousness. “The successor of Peter, the fisherman, is dying,” Chicago’s Cardinal Francis George said, holding back tears.
Church officials prepared the world and its 1.1 billion Roman Catholics for the end of the third longest papal reign in history - more than 26 years.
“The general conditions and cardio-respiratory conditions of the Holy Father have further worsened,” said Vatican spokesman Joaquin Navarro-Valls. “The biological parameters are notably compromised.”
Roman Cardinal Camillo Ruini said the Pope “already sees and touches the Lord. He is already united with our sole Saviour.” He was presiding over Mass at the Basilica of St John Lateran, the Pope’s cathedral as Bishop of Rome.
Father Konrad Hejmo, a close friend of the first non-Italian pope in 455 years, said the Pontiff was still alive but on oxygen.
Catholics flocked to churches to light candles and pray for the man who became Pope in 1978 and revitalised the papacy. Tens of thousands gathered in the Vatican’s vast St Peter’s Square, some gazing up at the papal apartments.
“This evening or tonight, Christ opens the doors to the Pope,” said Monsignor Angelo Comastri as he started a prayer vigil in the packed square.
After weeks of worsening health, the Pope developed a high fever on Thursday caused by a urinary infection. But he told aides he did not want to return to hospital, where he spent weeks before Easter after an attack of breathing trouble.
“The fact he has not gone back (shows) he is serenely carrying the cross and ready to give up and to say ‘It is finished’,” said Bishop of Cloyne John Magee, who served as the Pope’s private secretary from 1978 to 1982 and as master of pontifical ceremonies until 1987.
At a special vigil Mass in Armagh, the Primate of All Ireland, Cardinal Seán Brady, said he was very heartened to have received messages of support from leaders of other Churches.
“We all remember him with great affection and love,” he told a packed congregation.
Archbishop of Dublin, Diarmuid Martin, told the congregation at a Mass in Dublin’s Pro-Cathedral last night they should take inspiration from the way the Pope accepted his impending death.
“He was a Pope who showed enormous dynamism throughout his pontificacy. But there was no holding him back in his ministry, even until Wednesday last when against all advice he appeared at his window so as not to leave disappointed a large group of young people gathered in Saint Peter’s Square,” he told said
The Pro-Cathedral was packed with people saying prayers, with Taoiseach Bertie Ahern and Education Minister Mary Hanafin among them.
More than 800 people gathered at a vigil mass was held at the Basilica in Knock, where Pope John Paul prayed on his visit to Ireland in 1979. The parish priest of Knock, Monsignor Joe Quinn, said the Pope had a “special place in the hearts of the Irish people just as Knock held a special place in the heart of the Holy Father”.
Elsewhere, Poles clung to the hope their beloved countryman and moral authority would step back from the brink of death.
“I came to pray for the Pope,” said Maria Danecka, one of hundreds who crowded in and around the basilica in Wadowice, the town where Karol Wojtyla was born in 1920. Many of them wept.
Churches in the capital Warsaw and the southern city of Krakow where John Paul was once archbishop filled with worshippers.
The faithful said special prayers in Asia, Africa and the Americas.
Recent images of a gaunt, pained John Paul, his body ravaged by Parkinson’s disease and arthritis, contrast starkly with the sprightly Wojtyla who strode onto the world stage on October 16, 1978, and travelled the globe tirelessly.
The Pope came close to death before when a Turkish gunman shot him during a general audience in St. Peter’s Square in 1981.
After the Pope dies, more than 100 cardinals will be called to Rome to choose a successor at a conclave that normally starts in the Vatican’s Sistine Chapel 15 to 20 days after the death.
The Pope has grown steadily weaker over the past decade. He has been seriously ill for most of the past two months and failed to recover from a recent throat operation.
He has been unable to speak in public since he left hospital on March 13.
Historians say one of his legacies will remain his role in the fall of communism in Europe in 1989. His orthodox line on many Church teachings has won favour among poor-country Catholics but criticism from liberal believers.