The NT Government today said the couple flew into Darwin from a holiday in South Africa overseas on Silk Air flight MI801 from Singapore to Darwin on Saturday and then drove their own vehicle back to Katherine.

Anyone who traveled on these flights are asked to call the Public Health Unit on 08 8922 8044.

Twelve Territorians have now been diagnosed with COVID-19.

"They have been in self isolation in their own home," Health Minister Natasha Fyles said today of the Katherine couple.

Ms Fyles said the couple became ill and went to Katherine Hospital to be tested.

She said the Katherine couple had isolated themselves as required after returning to Katherine, other than the visit to the Katherine Hospital.

Coronavirus was confirmed late yesterday.

The had flown back from overseas on a Silk Air flight, the Minister said.

They are the first confirmed cases in the NT outside Darwin along with another couple from central Australia, one who is believed to be a policeman, who also tested positive yesterday.

The Katherine pair had just returned from overseas travel, Ms Fyles confirmed again today.

The four Territorians - a couple from Katherine and a couple from Central Australia - along with the Queensland woman transiting through Darwin had all returned from overseas travel.

All five people are under NT Health supervision.

Twelve Territorians have now been diagnosed with COVID-19. The Queensland woman's case will be recorded in that State's statistics.

Meanwhile, police have also set up internal road blocks across the Territory now the borders are officially closed.

Katherine Times understands travelers have been stopped between Mataranka and Katherine.

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