Catholic pilgrims have begun gathering in southern Poland ahead of the midweek arrival of Pope Francis for World Youth Day, a days-long gathering of young people.

Young people convened for prayers in Krakow on Monday, while thousands also visited the former Nazi death camp of Auschwitz-Birkenau.

On Friday, Francis will become the third pontiff to visit the somber memorial site, following in the footsteps of John Paul II and Benedict XVI.

Fatima Sonndevile, a pilgrim from Spain, said: "There is always light, and I think we have to find it. I think that is the reason pope sent us to (see) this ...to see what humanity did in the past, and try (to) not do it again."