The 79-year-old Argentinean Pope stumbled and then fell down out of view before being helped to his feet again by servers at the altar.
Francis seemed to be well as he delivered a sermon and said mass at the revered Jasna Gora monastery in the town of Czestochowa, in southern Poland.
Czestochowa is home to the renowned Black Madonna, an icon which faithful Catholics believe to have miraculous qualities.
Poland ups Pope security after Europe attacks
Security forces were on high alert at the hill-top shrine following a series of attacks in Europe, with a many police and army officials present on the roads leading into the southern Polish city.
Francis, the bishop of Rome, leapt into an open-topped popemobile for a tour through the cheering multitudes of people who had gathered to see him.
"We slept so little, but it's worth it, what an atmosphere!" said one pilgrim, Kate Tor, whose young sons were amongst the thousands of children who had camped out on the wide avenue leading to the monastery.
Adolescents draped with their sleeping bags, elderly couples sitting on folding chairs outside tents and families with Francis-themed balloons were entertained by the Argentine pope's favorite tango music before his arrival.
Ambulances and fire engines were on standby at all times, with Polish officials taking absolutely no risk with security following the murder of a priest in a French church, claimed by the Islamic State group, on the eve of the pope's five-day trip to celebrate the 2016 World Youth Day.
Just shortly after landing in Poland, Francis said the world was at war but argued that religion was not the cause, insisting the way for people to "overcome fear" was to provide refuge to those escaping war and conflict.
Pope says attacks shows "world is at war", religion not to blame
Francis left Czestochowa on Thursday by helicopter, heading back to Krakow, Poland’s second largest municipality, where he will be presented with the keys to the city, before hopping on to a tram which will whisk him off to the expansive Blonia meadow for his first big WYD event.
"Now go and do your duty, make noise all night long!" he finished his speech with a smile.
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