Vatican City - Catholic cardinals from around the world agreed on Monday to begin a conclave on May 7 to elect a new pope, and highlighted clerical sexual abuse as one of the key challenges facing Pope Francis' successor.

Cardinals under the age of 80 will meet in the Sistine Chapel to choose a new leader for the world's 1.4 billion Catholics, in a mystery-shrouded ritual dating back to the Middle Ages.

The date was decided at a meeting of cardinals of all ages early on Monday, two days after the funeral of Francis, who died on April 21 at the age of 88.

The cardinals, known as "Princes of the Church", outlined Catholicism's most pressing challenges, including "evangelization, the relationship with other faiths [and] the issue of abuse", the Vatican said.

Canada Driver plows into Vancouver festival crowd, killing multiple people

"There was talk of the qualities that the new pontiff must possess to respond effectively to these challenges," it added.

The Church's 252 cardinals were recalled to Rome after the Argentine pontiff's death, although only 135 are eligible to vote in the conclave.

They hail from all corners of the globe, and many of them do not know each other.

But they already had four meetings last week, so-called "general congregations", where they began to become better acquainted.