Fragments of the coronavirus have been found in Katherine's wastewater as the Northern Territory's first community outbreak rolls on.

Northern Territory officials are concerned COVID-19 could still be spreading in the community after wastewater testing found coronavirus fragments in Katherine.

Chief Minister Michael Gunner declared the emergency over on Monday, saying the Top End's first community outbreak was under control.

But that could have been premature after the positive wastewater tests in the town 320km south of Darwin.

"There's no need for residents to be alarmed but they do need to be very careful," Health Minister Natasha Fyles told reporters on Wednesday.

Katherine was plunged into a four-day lockdown a week ago when an infected 26-year-old man brought the virus to the town.

Two of his housemates fell ill, along with a 21-year-old woman who brought COVID-19 to the territory from Victoria.

Ms Fyles said all close contacts of the man would now be retested.

She also urged people to get a test if they developed symptoms but said there were no plans for additional health restrictions for the town.

"People don't need to panic," she said.

"We're not going to go into a lockout or a lockdown."

Residents must wear a face mask in most public places until Friday.

One new case was diagnosed in the NT overnight but it is not linked to current outbreak, Ms Fyles said.

A 20-year-old man from Victoria has tested positive for the virus after flying to Darwin via Sydney.

The man is a member of the Australian Defence Force and went straight into quarantine at Bladin Village Quarantine Facility after he arrived in the territory on Monday.

"There is a very low risk to Territorians," Ms Fyles said.

The man is expected to be transferred to Centre for National Resilience.

It comes as the Northern Land Council mandates COVID-19 vaccination for all workers and permit holders planning to travel to or wishing to remain on Aboriginal land in the Top End.

The new rules include transit, visitor, residential and recreation permit holders, in accordance with traditional owner wishes and NT health regulations, a spokesman said.

Like the NT chief health officer's direction, people who fall under the new mandate will have to have had at least one jab by Friday and be fully vaccinated by Christmas Eve.

There are about 8000 permits currently issued to a wide variety of workers, residents and visitors to NLC managed land.

They include schoolteachers, truck drivers, medical staff, media workers, contractors, miners, tour operators, tourists, community residents and their visitors.


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