It is hard to imagine the brawn of the Australian Border Force raiding the convent where Saint Mary MacKillop's body is entombed.

But that is the scenario North Sydney's Sisters of St Joseph will be preparing for on Sunday, as they ready to help harbour asylum seekers the Turnbull government tries to force back to Nauru or Manus Island.

Sisters Louise Reeves, Marion Gambin and Catherine Shelton from the Sisters of St Joseph. Credit:Dallas Kilponen

The order of Catholic nuns is among about 115 church groups across Australia that have formally offered to provide sanctuary or other aid to the asylum seekers – risking criminal sanctions and raids by police or border officials.

Almost 1200 religious leaders, people from their congregations and members of the public have registered for Sunday's training sessions in capital cities, to learn how to respond if authorities seek to enter church halls, vestries and other church buildings where asylum seekers have sought refuge.