Pope John Paul's fragile health stabilised yesterday after urgent medical treatment for severe breathing difficulties, but the Vatican said he would have to remain in hospital for the time being.
Chief spokesman Joaquin Navarro-Valls said the 84-year-old Pope, who was rushed to Rome's Gemelli hospital late on Tuesday, had needed help with his breathing overnight and was running a slight fever yesterday.
He added that the Pontiff would remain hospitalised "for a few more days", but stressed that he had never lost consciousness during the latest in a long line of health scares.
"I think everyone has to be calm because there is no reason for alarm today," said Mr Navarro-Valls, himself a doctor.
Italian Health Minister Girolamo Sirchia visited the Gemelli hospital later in the day and said the Pope was recovering. "He is improving, the doctors are optimistic," Mr Sirchia told reporters as he left the institute on the outskirts of Rome.
Catholics around the world - from the Pope's native Poland to the Philippines - attended special prayer services and as evening fell in Rome, the faithful gathered in St Peter's Basilica for a Mass the Pontiff had been scheduled to celebrate.
"The Holy Father thanks you for your affection and prayers. He is present here with us through prayer and he sends you his blessing," said the archbishop who took his place at the altar.
The prayers were for a man who left a mark like few others in the 20th century, playing a leading role in the fall of communism in Eastern Europe in 1989, travelling the world and working tirelessly to revolutionise ties with other religions.
The sudden illness of a Pontiff once known as "God's Athlete" because of his fitness raised inevitable speculation that one of the longest and most controversial papacies in history might be fading.
Although nearly all of the world's one billion Catholics have cheered his defence of human rights, the Pope has drawn criticism from within his own flock for his resolute opposition to contraception, gay marriage and women priests.
The Pope, who also suffers from debilitating Parkinson's disease, came down with influenza on Sunday, forcing him to cancel all public engagements at the start of the week.
His condition deteriorated rapidly on Tuesday with an acute attack of laryngospasm, a blockage of air to the lungs.
Medical experts said the ailment was rarely fatal, but cautioned that the Pope's age and frailty complicated matters.
"Advancing age brings with it increased risk of infection and with any illness, older people take longer to recover and the risks are greater," said Duncan Forsyth, a geriatrician and Parkinson's expert at Addenbrooke's Hospital in Britain.
Mr Navarro-Valls said that during the night the Pope had received "respiratory assistance therapy" that had "stabilised his clinical framework". He did not elaborate.
The Pope had rested "for several hours" and was able to participate in a mass from his hospital bed that was celebrated by his long-time Polish secretary.
While the Pope is in hospital, ordinary Vatican business will be taken care of by his inner circle. But they have no power to alter Church teachings on issues of faith and morals.