Pope John Paul II, determined to show the faithful he is recovering from his latest health crisis, appeared in an open hospital window yesterday and vowed to continue his mission despite his age and mounting medical troubles.

In a message read out by an archbishop, the 84-year-old pope looking rested and alert gave thanks for the prayers and affection he has received since he was rushed to Rome's Gemelli Polyclinic last Tuesday with breathing trouble brought on by the flu.

It was the world's first public glimpse of John Paul since his hospitalisation.

On St Peter's Square, where several thousand pilgrims and Romans gathered to see the pope on four giant video screens, cheers went up as his image filled the screens.

"Also in this hospital, in the middle of other sick people to whom my affectionate thoughts go out, I can continue to serve the church and the entire humanity," the pope said from the hospital in remarks read in Italian by Archbishop Leonardo Sandri, a Vatican official from Argentina.

"Today I speak to you from the Agostino Gemelli Polyclinic where I have been for a few days, being helped with loving care by doctors, nurses and health workers whom I thank from my heart," the pope's message said.

"May the expression of my gratitude for the sincere and heartfelt affection reach all of you, dear brothers and sisters, and to all those in every part of the world who are close to me, something which during these days I felt in a particularly intense way," he said.

The pope's message also spoke out anew against abortion urging people to "trust in the life that children who are not yet born silently cry out for".

"So many children, who are without families for various reasons, are asking for trust so that they can find a house that will accept them through adoption and temporary care," the pope said.

"To all and each of you I assure you of my gratitude, which is translated into a constant invocation of the Lord according to your intentions as also for the needs of the church and the great issues of the world," the pope said in his remarks.

Hospital workers watched with teary eyes as the pope sat quietly while he message was read, then gave his blessing and thanked those who had prayed for his recovery.

"It's always very moving," said Rory Conneely of Dublin, Ireland, among the thousands on St Peter's Square. "It's so sad he's coming to the end of his life."

The ANSA news agency reported that the pope's fifth night at the hospital passed calmly. Pilgrims also gathered yesterday outside the hospital, where a group of about 20 students from Spain stood vigil.

"We came today to pray with the pope, because he needs our prayers to make him feel better," said Blanca Bertran De Lis, a 17-year-old from the Spanish city of Toledo. "When young people are with him, he feels happier."

Police tightened security around the hospital, posting snipers on the roof over the pope's 10th-floor suite as officers checked trash bins and patrolled with bomb-sniffing dogs.