Dame Tariana Turia says Oranga Tamariki chief executive Grainne Moss should step aside and make way for Māori leadership.
The Māori Party says it's wrong that the most senior Māori leader at Oranga Tamariki is resigning from the ministry, and is calling for his boss to go instead.
Hoani Lambert has quit as the deputy head of Oranga Tamariki to take up a role at the Department of Internal Affairs.
But he insisted his departure was not a protest against the agency chief executive Grainne Moss.
"I was very grateful to Grainne who gave me my first opportunity to be the deputy chief executive in a government department. In that time we have established two Treaty units, we have begun the process of setting up strategic relationships with iwi and Māori organisations.
"I've also been given the privilege of establishing our first transition service - supporting young people who have spent a significant amount of their time in state care and right across the four years with her I've been very grateful other for the opportunities that she's given me," Lambert said.
Moss said the ministry was planning more partnerships with iwi. She was also open to the idea of working alongside a Māori chief executive of Oranga Tamariki.
"That's a wonderful idea."
The Waitangi Tribunal has been hearing from Moss as it investigates the ministry's role in uplifting Māori babies from their whānau.
The urgent hearing follows several other inquiries into the removal of babies and the overall performance of Oranga Tamariki.
Dame Tariana Turia was at the Waitangi Tribunal hearing yesterday.
Today she told Morning Report she knew Lambert for many years and his leaving was a "shock resignation".
Dame Tariana said yesterday Moss "kept on blaming the Crown" for the shortcomings at Oranga Tamariki.
"And I sat there wondering, who is the Crown? It is the minister. Is she saying that the minister's to blame? I couldn't quite work her out."
Dame Tariana said it was unusual for the head of any state agency to blame the Crown. "... [Moss] mentioned it more than once."
She did not have confidence in Moss and said if Lambert did, "he wouldn't be leaving".
"As far as I'm concerned why isn't the prime minister speaking if the Crown is the one who is at fault.
"This is an organisation that deals with 70 percent Māori children therefore deserves Māori leadership."
She said the government acknowledged that by appointing Kelvin Davis as Minister for Children.
"I think there is room for Grainne to be gracious and perhaps leave."
Davis has ordered Oranga Tamariki to stop carrying out 'reverse uplifts' - when a child in state care is taken away from their permanent foster parents and placed with whānau.
The order follows the recent Newsroom documentary that followed four tamariki who faced reverse uplifts.
A spokesperson for Davis confirmed a report into the incident had raised questions around some system-wide processes within Oranga Tamariki and wanted them reviewed.