Colourful groups of cheerful young pilgrims from around the globe are in the streets of Krakow, in southern Poland, just hours before Pope Francis arrives to join the celebrations of World Youth Day, a major gathering of Catholics.

It will be Francis' first visit to Poland, a predominantly Catholic country that is still proud of the late pontiff, St. John Paul II, who served as priest and archbishop in Krakow before becoming pope.

The sense of expectation was apparent in sunny Krakow on Wednesday with papal white-and-yellow flags decorating the streets and a heavy police presence.

The weather forecast for Krakow said rainstorms were possible later in the day.

Some 200,000 pilgrims attended an inaugural Mass Tuesday afternoon.