A report released on Tuesday concludes at least 3677 people were abused by clergy between 1946 and 2014.

Cardinal Reinhard Marx, who is also the head of the German Bishops Conference, said sexual abuse is a crime.

"I'm ashamed for so many (of us) looking away, not wanting to recognise what happened and not helping the victims," he told reporters.

"That goes for me as well."

The apology came on the day Pope Francis acknowledged that the sex abuse scandal rocking the Catholic Church was driving people away.

Francis said the church must change its ways if it wants to keep future generations.

The report on sex abuse in the German Catholic Church found that more than half of the victims were 13 or younger and most were boys.

Every sixth case involved rape and at least 1670 clergy were involved.

Some 969 abuse victims were altar boys.

On average, the abuses happened multiple times over a period of at least 15 months.

Although the German Bishops Conference released its report on Tuesday, it had already been leaked earlier this month and was heavily criticised for the lack of transparency and the church's refusal to let the researchers access original documents.

Instead of looking at the original church files, researchers sent questionnaires to the dioceses, which then provided the information.

The report was commissioned by the German Bishops Conference and researched by experts from the universities of Giessen, Heidelberg and Mannheim.

Australian Associated Press