Catholics around the globe are praying for Pope John Paul II, in hospital in Rome after breathing difficulties.
Thousands attended a candlelit mass in the Vatican
Despite the Vatican's attempts to quell alarm, special Masses have been hastily organised across the world.
Reflecting the appeal of the travelling Pope, famed for visiting more than 100 countries, Catholics in Mexico, Kenya and the West Bank have gathered.
Thousands have offered prayers for his speedy recovery from complications following influenza.
The Pope was admitted to a hospital in central Rome on Tuesday night but celebrated Mass from his hospital bed on Wednesday morning.
Thousands of faithful gathered in St Peter's Basilica in the Vatican - the Pope normally holds his weekly Wednesday audience from its square - for the feast of Candlemas.
Candles are lit and blessed to mark the day Jesus was presented to the temple 40 days after his birth.
It was a service that the Pope had intended to lead himself and the archbishop who took his place passed on a personal message from him.
"The Holy Father thanks you for your affection and prayers. He is present here with us through prayer and he sends you his blessing," he said.
In the Pope's native Poland, prayers were held at churches in Warsaw and Krakow, where Catholics lit candles.
In his hometown of Wadowice, they prayed at St Mary's Church where the young Karol Wojtyla was christened.
Former Polish President Lech Walesa said the Pope had already surprised many with his resilience.
In London, Catholics gathered in Westminster Cathedral
"Many had said the Pope was in bad shape and they are already with St Peter while the Holy Father continues to serve people and the world," he said.
In Mexico, a country visited by the Pope on no less than five occasions, Catholics gathered in the capital's cathedral.
"He gave us a lot of energy and life when he came to Mexico," worshipper Jorge Calderon told The Associated Press.
And in the Philippines, home to 65 million Catholics, the faithful packed into churches across the country, remembering his visits in 1981 and 1995.
Masses were also dedicated to the pontiff in the West Bank Church of the Nativity in Bethlehem.
"I am from Poland from the land of the Pope and we are in Poland always very close to the Pope and we pray always for him," said Polish priest Richard Kenpak, speaking at the church.