Church leaders offering sanctuary to asylum seekers who face being sent to offshore detention could be risking 10 years' jail, an academic working in migration law says.

Key points: Church leaders are offering sanctuary to asylum seekers facing offshore detention

Church leaders are offering sanctuary to asylum seekers facing offshore detention Providing sanctuary is a historical concept for churches

Providing sanctuary is a historical concept for churches Legal risks are involved for harbouring "an unlawful non-citizen, a removee or a deportee."

Legal risks are involved for harbouring "an unlawful non-citizen, a removee or a deportee." Penalty is imprisonment of 10 years, fine of $180,000, or both

Penalty is imprisonment of 10 years, fine of $180,000, or both Immigration Minister Dutton says churches are not above the law

Anglican Dean of Brisbane, the Reverend Dr Peter Catt, said he was opening up St John's Cathedral in Brisbane to some of the 267 asylum seekers who are in fear of being returned to Nauru or Manus Island.

The Australian Churches Refugee Taskforce said offers of help were coming from across Australia.

There were also questions about how much legal protection asylum seekers would have by sheltering in a church.

Marianne Dickie, a senior academic at ANU working in the migration law program, said that there was a section within the Migration Act that made it an offence to harbour a person deemed an unlawful non-citizen, a removee or a deportee.

"So [the penalty for] that offence is imprisonment of 10 years or fine of $180,000 or both," she said.

"But for us the problem arises with the term unlawful non-citizen, removee or deportee in determining what status the people that the church is saying that they'll look after, hold at that present time."

Misha Coleman, from the Australian Churches Refugee Taskforce, said the logistics of getting asylum seekers to the churches was difficult.

"To effectively provide sanctuary or to provide protection from harm you need to do that very quietly," Ms Coleman said.

"So it was a big decision for us to announce this publicly, but we wanted people to know that we are there for them."

Asylum seekers at risk of deportation 'seeking desperate measures'

Ms Coleman said the number of refugees who were in a position to even access the churches' offer of help is small.

She said there were 15 families living in the community across the four states that they were aware of, and they would be the people who could most easily enter one of the churches offering sanctuary.

"Those families that we're talking to, we're counselling them to get some really very in-depth advice from their own legal representatives about what the implications for them and their case and their application for a protection visa ultimately would be," Ms Coleman said.

She said she was unable to elaborate on how well those 15 families had been coping.

"I can say that people knew that the High Court case wasn't going to be something that would protect them," she said.

"Seventy-two hours' notice will be given, hopefully, of deportation to an offshore facility.

"So now that that prospect is really live ... people are absolutely in shock, devastated, and can I say, seeking desperate measures."

Providing sanctuary is a historical concept, but the legal risks involved for church members to offer it were real.

The Australian Churches Refugee Taskforce said they are hopeful the legal risks will not be put to the test.

However, Immigration Minister Peter Dutton told 2GB radio that churches were not above the law.

"Churches provide lots of assistance to refugees and they feel very strongly about this issue," he said.

"In the end, people have to abide by Australian law, regardless of who they are."