Nev Power and Mathias Cormann at Senate estimates (Image: AAP/Lukas Coch)

Where does the Department of Prime Minister and Cabinet (PM&C) end and the National COVID-19 Commission begin? 

That's the question being asked after another eye-opening appearance by commission chair, former Fortescue boss Nev Power, at Senate estimates yesterday.

Power, appearing alongside Finance Minister Mathias Cormann, faced questions about the commission’s high-level access to cabinet documents and ministers, including aboard Power’s private plane.