Pope Francis has urged young people to keep shouting and not let older generations silence their voices or “anaesthetise” their idealism.

Drawing on biblical parallels in front of tens of thousands in St Peter’s Square, many of whom were young people there for the Catholic Church’s World Day of Youth, the Pope urged youngsters to not let themselves be manipulated.

“The temptation to silence young people has always existed,” the 81-year-old said.

“There are many ways to silence young people and make them invisible. Many ways to anaesthetise them, to make them keep quiet, ask nothing, question nothing.

“There are many ways to sedate them, to keep them from getting involved, to make their dreams flat and dreary, petty and plaintive.”

“Dear young people, you have it in you to shout,” he said, urging youngsters to be like the people who welcomed Jesus with palms rather than those who shouted for his crucifixion.

Pope Francis arrives in procession at St Peter’s Square during the Palm Sunday Mass (Getty Images/Franco Origlia)

“It is up to you not to keep quiet. Even if others keep quiet, if we older people and leaders, some corrupt, keep quiet, if the whole world keeps quiet and loses its joy, I ask you: will you cry out?”

The young people in the crowd shouted “yes”.

Carrying a woven palm branch known as a “palmurello”, the Pope led a procession to commemorate the day the Bible says Jesus rode into Jerusalem and was hailed as a saviour, only to be crucified five days later.

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While he did not mention Saturday’s marches in the United States, he has often condemned weapons manufacturing and mass shootings.

Palm Sunday marked the start of a hectic week of activities for the pope.

On Holy Thursday he is due to be at two services, including one in which he will wash the feet of 12 inmates in a Rome jail to commemorate Jesus’ gesture of humility towards his apostles the night before he died.

A view of St Peter’s Square as Pope Francis celebrates Palm Sunday Mass at the Vatican, urging young people not to be silent and let their voices be heard (AP/Angelo Carconi) (AP)

On Good Friday, he is due to lead a Via Crucis (Way of the Cross) procession at Rome’s Colosseum.

On Saturday night he will lead an Easter vigil service, and on Easter Sunday he delivers his twice-yearly ‘Urbi et Orbi’ (to the city and the world) message.