Pope Francis falls at altar during televised Mass in Poland

The 79-year-old tripped on a step but did not appear to be injured

Pope Francis fell over at the start of Mass on Thursday while visiting Poland’s holiest icon, the Black Madonna of Jasna Gora.

His stumble took place in front of a congregation of thousands and a television audience of millions.

Francis suffers from sciatica, a medical condition in which pain sometimes shoots down the leg from the lower back.

The 79-year-old was helped up by aides after tripping on a step and did not appear to be injured - conducting Mass as usual.

Francis urged Poland to remain united over issues such as the refugee crisis, praying people have "the desire to leave behind all past wrongs and wounds, and to build fellowship for all, without ever yielding to the temptation to withdraw or to domineer."

The Mass was held in celebration of the 1,050th anniversary this year of the Poland's acceptance of Roman Catholicism.

The main event is an international gathering of Catholic youth in Krakow which has sometimes been dubbed the “Catholic Woodstock.”