Tasmania's Governor, Peter Underwood, AC, is gravely ill after a kidney cancer operation, the state's Government House said on Monday.
Mr Underwood, 76, suffered a significant setback last week following the operation in June, and was being monitored with great care in Royal Hobart Hospital, a statement said.
Appointed Governor in 2008 and recently reappointed for a further term, Mr Underwood had previously served as Tasmania's Chief Justice.
He drew controversy in April with a speech that said Australia needed to drop the sentimental myths that Anzac Day had attracted, instead advocating a year of peace for the centenary of World War I.
Justice David Porter has been appointed Administrator in his stead until July 19, the statement said.
The statement said updates on Governor Underwood's condition would be provided by his office as they become available.
The Anglican Bishop of Tasmania John Harrower has taken to Facebook to ask people to pray for his recovery.
- with AAP