Pope Francis has urged "drowsy and dull kids" to swap their sofas and video games for walking boots at an international Catholic youth festival in Poland.

Key points: Pope says sofa gives children false sense of safety, television numbs youngsters to suffering of others

Pope says sofa gives children false sense of safety, television numbs youngsters to suffering of others Says children should get out of their living rooms

Says children should get out of their living rooms Comments come amid World Youth Day celebrations

He warned lounge chairs gave the illusion of safety from pain, fear or worries, allowing the sitter to kick back and lose themselves for hours in the latest television show or their smartphones.

"For many people it is easier and better to have drowsy and dull kids who confuse happiness with a sofa," he told an estimated one million people gathered at a vigil in a vast plain near Krakow.

"Dear young people, we didn't come into the world to vegetate ... we came for another reason: to leave a mark.

"The times we live in do not call for young 'couch potatoes' but for young people with shoes, or better, boots laced."

Pope Francis, 79, said being constantly glued to screens — where the terrible events of the world become just another story on the evening news — numbed youngsters to the suffering of others.

He prayed for war-torn Syria, quoting a pilgrim from the city of Aleppo who had testified before the Pope and crowds of the fight between life and death in her "forgotten city".

"Our response to a world at war has a name: fraternity," he said.

The pontiff arrived in Poland on Wednesday and yesterday took a tour of Auschwitz, where he met with Holocaust survivors.

His visit came a day after the jihadist murder of a priest in France and in the wake of a series of attacks in Europe.

He said the attacks were proof that "the world is at war".

Pope Francis walked through the gate of Auschwitz, the former Nazi German concentration camp, in silence. ( Reuters: Kacper Pempei )

AFP