The killing of an 85-year-old priest in a Normandy church yesterday added to security fears surrounding Francis' five-day visit for the World Youth Day celebrations, which were already high due to a string of violent attacks in France and Germany.
Polish officials say they have deployed tens of thousands of security officials to cover the event.
Francis spoke to reporters on the papal plane en route from Rome to Poland.
Upon arrival at Krakow airport a pensive Francis was greeted by Poland's President Andrzej Duda, First Lady Agata Kornhauser-Duda and other state officials, and hundreds of faithful who had waited for hours to see him.
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The main welcoming ceremony with speeches is to be held later in the day at the Wawel Castle in Krakow.
In the evening Francis is to appear in the window of the residence of Krakow bishops, where he will be staying, and chat with some among the hundreds of thousands of pilgrims from around the world gathered for the World Youth Day celebrations that will run through Sunday.
"Let's live WYD (World Youth Day) in Krakow together!" the pontiff tweeted before departing from Rome for Krakow, southern Poland, this afternoon.
Relics of St. Mary Magdalene came to the church from France, for the duration of World Youth Day, and were displayed in a case by the altar.