The Pope opened the summit on Thursday by praying for help turning "this evil into a chance for understanding and purification."

In a short opening statement, he said Catholics and victims were expecting not simple, predictable condemnations but "concrete and efficient measures".

He told the gathering of 190 leaders of bishops' conferences and religious orders that they bore the responsibility to "listen to the cry of the young who want justice."

He also called on the Virgin Mary to "enlighten" bishops in their attempts to "heal the grave wounds that the pedophilia scandal has inflicted both on children and on the faithful."

Francis called the summit after botching a well-known sex abuse cover-up case in Chile last year. Realising he had erred, the Pope vowed to chart a new course and is bringing the rest of the church leadership along with him.

More than 30 years after the scandal first erupted in Ireland and Australia and 20 years after it hit the US, bishops and other Catholic superiors in many parts of Europe, Latin America, Africa and Asia either deny that clergy sex abuse exists or downplay the problem.

The summit is meant as a tutorial for church leaders to learn the importance of preventing sex abuse in their churches, tending to victims and investigating the crimes when they occur.

Abuse survivors have turned out in droves to demand accountability and transparency from church leaders, saying the time of cover-up is over.

Phil Saviano, who helped expose the US scandal two decades ago, demanded the Vatican release the names of abusers and their files.

"Do it to break the code of silence," he told the organising committee on the eve of the summit. "Do it out of respect for the victims of these men, and do it to help prevent these creeps from abusing any more children."

Australian Associated Press