The Northern Territory's chief health officer is in COVID-19 quarantine at the Howard Springs facility.
Hugh Heggie was travelling in Victoria when the NT declared Greater Melbourne a hotspot on Thursday.
Dr Heggie returned to Darwin and is undertaking mandatory, supervised quarantine at the former mining camp on Darwin's outskirts.
Dr Charles Pain will continue as acting chief health officer while Dr Heggie isolates.
Earlier, a COVID-19-infected Australian repatriated from Timor-Leste was admitted to the intensive care unit at Royal Darwin Hospital.
The Northern Territory responded to a request to accept the COVID-positive Australian citizen on humanitarian grounds, NT Health said.
"We have one individual being cared for in ICU," NT Health Minister Natasha Fyles told reporters on Friday.
"An Australian at Royal Darwin Hospital who did get repatriated in from Timor-Leste.
"My understanding is there was no cost to the taxpayer for that repatriation."
The patient remains in the care of RDH in a stable condition, NT Health said in a statement.
The case is not included in NT coronavirus data because the patient wasn't infected or diagnosed in the Territory.
RDH has just two ICU beds available to patients infected with COVID-19.
Ms Fyles and NT Health declined to answer questions about the patient and would not confirm how long the person had been undergoing treatment.