Pope Francis has urged princes, presidents, sheikhs and thousands of ordinary people gathered for his installation Mass to protect God's creation, the weakest and the poorest of the world.

He is officially beginning his ministry as the 266th pope with a clear focus of his priorities.

Francis was interrupted by applause several times during his homily today, including when he spoke of the need to protect the environment and serve one another with love and tenderness and not allow "omens of destruction," hatred, envy and pride to "defile our lives."

Francis said the pope "must open his arms to protect all of God's people and embrace with tender affection the whole of humanity, especially the poorest, the weakest, the least important."