Pope Francis has permanently removed a Polish bishop who was kicked out of his diocese a few months ago pending a Vatican investigation into allegations he covered up cases of sexual abuse by his priests.

The resignation of Edward Janiak as bishop of Kalisz suggests the Vatican was able to substantiate at least some elements of the accusations made in a documentary about sex abuse in Poland that has undermined the country's influential Catholic hierarchy.

Francis on Saturday accepted the bishop's resignation and confirmed the archbishop of Lodz, Grzegorz Rys, as the diocese's temporary administrator.

At 68, Mr Janiak is well below the normal retirement age of 75 for bishops.

Francis in June had ordered Mr Janiak to leave Kalisz and forbade him from having any influence on how the diocese is run pending the investigation.

In May, the online documentary Playing Hide And Seek exposed two cases of paedophile priests that Mr Janiak handled, first as an auxiliary bishop of Wroclaw and then as bishop of Kalisz, which he had headed since 2012.

It featured court evidence about Mr Janiak's role in helping transfer one priest, subsequently convicted and defrocked, from Wroclaw to another diocese even after a criminal investigation had begun.

The film also documented an alleged cover-up relating to another priest during Mr Janiak's time as Kalisz bishop.

The film was the second on Polish clergy abuse to be made by brothers Tomasz and Marek Sekielski.

Their first film last year, Tell No One, triggered a national reckoning in a country where there is no higher moral authority than the Catholic Church and its clergy.