The Northern Territory has recorded two new COVID-19 cases as the first Top End health worker is diagnosed with the virus.
It brings the territory's latest outbreak to 21 after a 33-year-old man and a 59-year-old woman became infected.
"The male is a health worker who initially had contact with an earlier positive case," Chief Minister Michael Gunner told reporters on Friday.
"He is, I believe, the first health worker in the territory to be positive for COVID-19.
"The man was fully vaccinated, however, he also has other existing health issues so he has been transported to Royal Darwin Hospital."
The woman has been linked to one of the households where other cases in the current cluster live.
Both new cases are from Katherine, 320km south of Darwin.
Wastewater results from across the territory have come back negative except in Katherine and Howard Springs, where The Centre for National Resilience quarantine facility is located.
The virus was also detected in an Aboriginal community of about 200 people on Katherine's outskirts.
Health workers are now vaccinating and testing residents.
"We are feeling okay but we are still not completely confident that we have this thing contained," Mr Gunner said.
Meanwhile, genomic testing has confirmed the territory's current outbreak was triggered by an infected woman who illegally entered the NT.
The 21-year-old lied on her border entry form late last month before travelling from Cairns to Darwin after visiting Victoria, where she'd contracted the virus.
She infected a man she spent time with in Darwin and the virus spread to two others in Katherine before authorities declared they had control of the outbreak on 9 November.
But that was short-lived, with the same strain of virus now found to be responsible for the current cluster.
Health teams are now attempting to find the missing links between the two clusters, with Mr Gunner saying it was a "strange mystery".
"We still don't know how it went from that small first cluster to no cases for nine days, then a second cluster that came from the first," he said.
"There is a very real possibility that there are people in Katherine who have COVID and either don't know it or don't want to know it.
Mr Gunner said it was possible the virus had been silently spreading and many more cases could be detected in the coming days.
The current outbreak started when a 30-year-old woman and a 43-year-old man from Katherine, 320km south of Darwin, became infected.
The woman was unvaccinated and travelled from Katherine to Robinson River - 1,000km southeast of Darwin - where she tested positive, the first case reported in a remote NT Aboriginal community.
Nine new cases were detected in Katherine on Tuesday, including a 71-year-old man and a 65-year-old woman who was admitted to Royal Darwin Hospital.
Eight new cases were reported on Wednesday, with five infections diagnosed in Robinson River, including a three-week-old girl.
No new cases were recorded on Thursday.
Greater Katherine and Robinson River are currently under a seven-day lockdown order, which is scheduled to end late Monday.
Mr Gunner said a territory-wide health order to wear face masks in most public places until Monday will be reviewed on Saturday.
