Chief Minister Michael Gunner announced on Monday afternoon that a 43-year-old Aboriginal man tested positive to the virus on Saturday, with authorities treating him like he's been infectious since November 10.

The fully-vaccinated man lives with seven other people in Katherine East.

One of his household contacts, a 30-year-old unvaccinated Aboriginal woman, tested positive to the virus in the remote community of Robinson River today.

The woman flew into the community, near Borroloola, on November 11, with authorities treating her as having been infectious since this date.

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The Katherine wider region, and well as Robinson River and its nearby homelands will go into a 72-hour lockdown from 6pm tonight.

It is unclear if these two new cases are connected to the previous Katherine-Darwin cluster

Mr Gunner said Robinson River, with a population of around 350, has a relatively high vaccination rate of 77 per cent first dose and 87 per cent fully-vaccinated.

He said a "rapid assessment team" is making their way to Robinson River tonight to conduct a testing and vaccination blitz.

Extra vaccinations will also be made available in Borroloola, although there is no lockdown planned for Borroloola.

"This is undoubtably the most serious update I've had to give you since the start of the pandemic because it involves a case in a remote community, but we are very prepared for this," Mr Gunner said.

"It's not the scenario we wanted, but we knew the day would come.

"We're establishing contact with each of these homelands now and advising people stay where they are. If they need anything, we will organise that."

Mr Gunner also said the most recent wastewater results conducted in Katherine have come back positive for both catchments in Katherine.

Acting Chief Health Officer said authorities were concerned about a potential COVID case in Katherine for "a few days now."

"The only way we can be confident of tracking this down is if everyone cooperates to the full extent with the restrictions we are putting in place to get tested and get vaccinated."

He said the vaccination rate in Katherine town is "around 80 per cent."

"But it's it's not so much Katherine that we're concerned about in terms of vaccination rates, it's about the potential transmission outside of Katherine through Aboriginal communities."

Anyone with any symptoms in either the Katherine or Robinson River regions or who has been in these areas is urged to get tested for COVID-19.

"Everybody knows when they've got respiratory symptoms, please come forward and get tested now so we can track this down," Dr Pain said.

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