The man arrived in the Northern Territory on a flight from Melbourne on Friday.

He is now under the care of the local health services while all close contacts, including some people on the same flight, are now in mandatory supervised isolation at Howard Springs Quarantine Facility.

His case takes the total number of COVID-19 infections reported in the NT to 33, all related to international or interstate travel.

Meanwhile, three men and a woman are in isolation in Alice Springs as authorities investigate if they arrived in the Territory from a coronavirus hotspot.

The men - aged 26, 27 and 29 - and the 28-year-old woman travelled to the Northern Territory by road, passing through a control point on the Territory-Queensland border on Monday.

But police said information received from a member of the public indicated the three men may have travelled from a declared COVID-19 hotspot in the previous 14 days.

The NT has declared all of Victoria and the greater Sydney area virus hotspots, forcing anyone who arrives from those regions into 14 days of supervised quarantine at their own expense.

The four people are being held in quarantine while three other people they had close contact with have also been placed in isolation.

COVID-19 testing and further contact tracing in relation to all seven is underway.

Australian Associated Press