Pope John Paul II's (search) condition is "very serious" but the pontiff is responding to members of his staff, the Vatican said in its latest update Saturday evening.

"The clinical conditions of the Holy Father remain very serious. In late morning, the high fever developed. When addressed by members of his household, he responds correctly," the Holy See said in a written statement issued around 7:30 p.m. (12:30 p.m. EST).

The 84-year-old pontiff was reported to have had a fever on Thursday night which the Vatican blamed on a urinary tract infection that later led to heart and kidney problems. The statement did not say whether the fever had subsided at any time since or whether Saturday morning's fever was a new bout.

At about the time the communique was issued, a light went on in the pope's third-floor apartment overlooking St. Peter's Square (search), drawing applause from the estimated 50,000 people keeping vigil there. The papal apartment kept five lighted, open windows — a sign that the pontiff was still alive and that the Vatican Secretary of State was continuing the activities of the church.

Tourists and pilgrims streamed anew into St. Peter's Square Saturday evening for a prayer vigil, many arriving with sleeping bags. Young people placed votive candles and a banner on the ground with the logo for World Youth Day, which will take place in mid-August in Germany. They spelled out the words "Con Te," or "With You," a poignant reminder of the one foreign appointment the pope had hoped to keep this year.

In an earlier briefing Saturday morning, Vatican spokesman Joaquin Navarro-Valls had said that the pontiff had shown signs of losing consciousness, but that he was not in a coma. A mass was held in the pope's presence early Saturday, but John Paul II did not concelebrate the rite, the spokesman said.

Navarro-Valls also added that when aides told the pope that thousands of young people had gathered in St. Peter's Square, the ailing pontiff seemed to refer to the crowds, saying something to the effect of: "I have looked for you. Now you have come to me. And I thank you."

John Paul II was last seen in public on Wednesday when, looking gaunt and unable to speak, he briefly appeared at his window.

His health sharply deteriorated the next day after he suffered a urinary tract infection. The Vatican said the pope was suffering from septic shock, which involves both bacteria in the blood and a consequent over-relaxing of the blood vessels.

The vessels, which are normally narrow and taut, get floppy in reaction to the bacteria and can't sustain any pressure. That loss of blood pressure is catastrophic, making the heart work hard to compensate for the collapse.

Medical experts put the chances of survival for an elderly person in John Paul's condition at no more than 20 percent, and only when hospitalized in intensive care. John Paul has chosen to remain at his Vatican studio.

The pope was being helped by his personal doctor, two intensive care doctors, a cardiologist, an ear, nose and throat specialist and two nurses.

A workman in the square, declining to give his name, told The Associated Press that crews were taking down the canopy on the steps of St. Peter's Basilica, which had covered an altar during Easter Sunday Mass, because they had orders to clear the space for when the pope's coffin eventually is carried into the square.

In a sign of respect for the pope's illness, Italy's highest sport authority on Saturday suspended all weekend events, including all Serie A soccer games.

Early Saturday the bronze door off of the sprawling plaza reopened to allow the faithful to morning Mass — one sign among many that the pope was still alive.

One of the pope's closest aides, Cardinal Joseph Ratzinger (search), was quoted Saturday as saying that when he saw the pontiff on Friday morning, John Paul was "aware that he is passing to the Lord."

The pope "gave me the final farewell," the news agency of the Italian bishops conference quoted the German cardinal as saying Friday night.

In another sign of the pope's decline, several cardinals said they were heading to Rome, including Roger Mahony, archbishop of Los Angeles, and William Keeler, archbishop of Baltimore, Maryland. After the official mourning period following the death of the pope, cardinals hold a secret vote in the Sistine Chapel to choose a successor.

President Bush on Saturday said that Pope John Paul II was "a faithful servant of God and a champion of human dignity and freedom."

"He is an inspiration to us all," Bush said in his weekly radio address. "Laura and I join millions of Americans and so many around the world who are praying for the Holy Father."

The president has received regular briefings about the pontiff's condition since the pope's health began deteriorating.

Newspapers in Italy devoted most of their Saturday editions to the suffering of the 84-year-old pope. Il Tempo showed a photo of the white-clad pontiff with his back turned to the camera, with the headline, "Ciao, Karol."

The Il Secolo XIX newspaper of Genoa reported that the pope, with the help of his private secretary Archbishop Stanislaw Dziwisz (search), wrote a note to his aides urging them not to weep for him.

"I am happy, and you should be as well," the note reportedly said. "Let us pray together with joy."

A Vatican cardinal, Achille Silvestrini, visited John Paul on Saturday morning, accompanied by another cardinal, Jean-Louis Tauran, and spoke of the pope's "slow death throes."

"I found him relaxed, placid, serene. He was in his bed. He was breathing without labor. He looked like he lost weight," Silvestrini said.

He said when he and Tauran came into the room, the pope seemed to recognize them.

"The pope showed with a vibration of his face that he understood, indicating with a movement of his eyes. He showed he was reacting," he added.

In Kuria Square in Krakow, Poland, other supporters gathered outside a yellow house where the pope once lived for a vigil Mass, and they paid tribute in his birth town of Wadowice. And in the United States, churches across the country held their own Masses for Pope John Paul II.

As the medical developments unfolded, the pope's followers attended a large Mass for him at the church of Santa Giovanni in Laterano in Rome, led by Cardinal Camillo Ruini, the pope's vicar, who is charged with making the formal announcement of the pope's death when it occurs.

Muslims in France were praying for the pontiff because he was a "man of peace," said Dalil Boubakeur, president of the French Council of the Muslim Faith. And in New York, Rabbi James Rudin told FOX News that the Jewish community would remember this pope with fondness because of his longstanding fight against anti-Semitism.

"He constantly denounced anti-Semitism," said Rudin, religious advisor at the Center for Catholic-Jewish Studies. "He was the first pope who said Jews are our elder brothers in faith."

Rudin called John Paul's efforts to unify the Catholic and Jewish communities "historic" and spoke of the pope's own personal experience with anti-Semitism during the Holocaust in his hometown in Poland.

Washington, D.C.'s Cardinal Theodore McCarrick (search) seemed in good spirits as he made comments to reporters Friday afternoon, saying he planned to travel to Rome on Sunday.

"We're delighted at the outpouring of interest and concern in the Holy Father," he said.

Asked to comment on the future of the Catholic church in the United States, McCarrick described the recent turmoils as "a purification, but purifications are good."

Hospitalized twice last month following two breathing crises and with a tube placed in his throat to help him breathe, John Paul has become a picture of suffering. When he appeared at his apartment window Wednesday to bless pilgrims in St. Peter's Square, he managed to utter only a rasp. Later that day, the Vatican announced he had been fitted with a feeding tube in his nose to help boost his nutritional intake.

On Friday evening, Italian media backed away from reports that the pope had died.

Earlier Friday, the pope lost consciousness, his breathing was shallow and his kidneys were also apparently failing. Some Italian wire and television sources reported just before 9 p.m. that the pontiff's heart and brain activity had stopped and a monitor on a machine had displayed a flatline, but they reversed that proclamation after Vatican sources said it wasn't true and there was no such machine in the pope's apartment.

The use of the feeding tube illustrates a key point of Roman Catholic policy John Paul has proclaimed: It is morally necessary to give patients food and water, no matter their condition.

As Parkinson's disease and other ailments have left him increasingly frail, the pope has been emphasizing that the chronically ill, "prisoners of their condition ... retain their human dignity in all its fullness."

The Vatican's attitude to the chronically ill has been apparent in its bitter condemnation of a judge's order two weeks ago to remove a feeding tube from Terri Schiavo, the severely brain-damaged American woman who died Thursday.

John Paul's 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 pope has no close relatives, but the Vatican has officially declined to comment whether John Paul has left written instructions.

FOX News' Greg Palkot and The Associated Press contributed to this report.