Organisers at the Lourdes shrine passed out water bottles and urged pilgrims to protect themselves against the hot sun today as they gathered for Pope John Paul's open-air Mass.
Temperatures in this southwestern French mountain town were due to rise to over 30 degrees centigrade for the principal event in the 32-hour visit of the 84-year old pontiff, who was exhausted by the few appearances he made here yesterday.
The Pope was literally "an ill man among the ill" yesterday, at one point nearly collapsing as he knelt at the grotto where the Virgin Mary was said to have appeared in 1858. The two-hour Mass in today's heat should prove gruelling.
"We cannot tell you enough that you must drink water, cover your heads and wear sunglasses," priests at Europe's most popular pilgrimage site announced to the waiting faithful in several languages.
After Mass and an afternoon rest, the Pope will say one last prayer to the Madonna and return to Rome in the early evening. His visit falls on the Feast of the Assumption, when the Church says the mother of Jesus Christ was brought bodily into Heaven.
His strength fluctuated visibly on Saturday, leaving him strong enough to remind secular France of the Church's role in society but too weak to lead prayers at the famous grotto.
A long procession of candle-carrying pilgrims cheered their encouragement on Saturday evening as John Paul, who is stricken with Parkinson's disease, struggled to read out a short address to them. His words were barely intelligible.
"With you I share a time marked by physical suffering, yet not for that reason any less fruitful in God's wondrous plan," he said at one point, stressing his attachment to all sufferers rather than asking relief from his own ailments.
About six million visitors flock to Lourdes each year, many of them ailing people who pray for miracle cures as they drink holy waters. The Church vets each claim of sudden healing carefully and has recognised 66 cases as miracles.
Church officials have estimated that up to 300,000 people would turn out for the Mass, about twice the crowd that gathered yesterday for his arrival and the public recitation of the rosary, a traditional Catholic series of prayers to the Madonna.
This trip was John Paul's 104th foreign tour and his second to Lourdes, which he first visited in 1983.
He has been a lifelong devotee of the Virgin Mary and will visit another Marian shrine in Loreto, Italy next month.