Wastewater testing reveals the virus could have spread to a second Aboriginal community after fragments were detected at Binjari, near Katherine.

Close contacts have been identified in Central Australia in the remote community of Yuendumu, 1600km south of Darwin.

The new cases bring 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.

Mr Gunner said the man was the first NT health worker infected with the virus.

"The man was fully vaccinated, however he also has other existing health issues so he has been transported to Royal Darwin Hospital," he said.

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 containing COVID-19 has been found in Katherine, Howard Springs, where a quarantine facility is located, and now the Binjari Aboriginal community in Katherine's outskirts, where about 200 people live.

Four new close contacts have been identified, three in Yuendumu and one in Tennant Creek, 1000km south of Darwin.

Health workers are vaccinating and testing residents in the communities.

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 had contracted the virus.

The woman left the NT after she was fined $5024 for breaching a health order but Police Commissioner Jamie Chalker says she could now face fresh charges.

She infected a man in Darwin and the virus spread to two others in Katherine before authorities declared they had control of the outbreak on November 9.

But that was short-lived, with the same strain of virus now found to be responsible for the current cluster.

Health teams are 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 became infected.

The woman was unvaccinated and travelled from Katherine to Robinson River, 1000km southeast of Darwin and 800km east of Katherine, 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. All the infected people are Indigenous Territorians.

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.

NT Health says 82 per cent of people in Katherine over 16 have had their first vaccine dose and 75 per cent are fully vaccinated.

Its statistics have previously been criticised for being inflated by about 10 per cent.

Australian Associated Press