A traveller from Cairns, who spent two nights with a man since diagnosed with COVID-19, could be the source of a Top End outbreak.

A traveller from Queensland could be the source of the Northern Territory's first community transmission of COVID-19, as a second case is diagnosed in the Top End.

Health workers are racing to find additional contacts, with a three-day lockdown in Katherine and lockout in Greater Darwin scheduled until midnight on Sunday.

The new case is housemate of an unvaccinated man in his 20s who was diagnosed in Katherine, 320km south of Darwin, on Thursday.

Chief Minister Michael Gunner says that man stayed at the Mantra Hotel in Darwin with a traveller from north Queensland after visiting the Monsoons pub and nightclub.

"We do know that he spent time on Friday and Saturday night with a person who had recently arrived from Cairns," he told reporters on Friday.

"So we are investigating that further and that person is now in quarantine and we are interviewing them to determine if this is the source."

Mr Gunner said the man was likely to be infected with the Delta variant and he could have been infectious in the community from Sunday until Tuesday, when he started developing symptoms.

"This makes COVID real for alot of Territorians," he said.

The infected man lives in a rural area south of Darwin and works at the Tindal air force base near Katherine, but that site is not considered an exposure site.

Defence doesn't require its members or contractors to be vaccinated to enter and work at the base.

The man moved about Darwin and Katherine before he was tested on Wednesday.

He is quarantining at the National Centre for Resilience at Howard Springs, where he is assisting health workers with contact tracing.

All told, 75 close contacts have been identified, with 48 contacted and order to quarantine for 14 days.

Multiple close and casual exposure sites have been listed, including the Katherine Club, Equinox Fishing Charter and Katherine Woolworths.

Monsoons is a location of concern.

Katherine went into lockdown for 72 hours at 12.01am (local time) on Friday.

Greater Darwin also had health restrictions imposed, with its first lockout for unvaccinated people.

Under the new rules, only fully vaccinated people are permitted to move about the community so long as they wear a face mask and show their vaccination certificate.

Mr Gunner previously said Katherine was locked down because its vaccination rate was below 80 per cent double-dosed.

Seventy-five per cent of eligible residents have had their first dose and 65 per cent are fully vaccinated.

Across the NT, 78 per cent of people aged 16 and over have had one dose and 65 per cent have had two jabs, according to federal government data.


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