A child from Wuppa Town Camp in Tennant Creek and a man and woman in their 30s from Walkabout Bore, 615km to the south, have tested positive.
"All of these cases are connected back to the Katherine cluster," Acting Chief Minister Nicole Manison told reporters on Monday.
It brings the current outbreak to 112 cases with more expected.
The outbreak started when an infected woman illegally entered the NT in late October.
The 21-year-old was fined for lying on her border entry form as the virus spread south from Darwin to Katherine, then to multiple Aboriginal communities.
Police have since launched a fresh investigation into the border breach after an Aboriginal woman died from COVID-19 in early December.
The infected man and woman were in Tennant Creek last week and tested positive at Alice Springs Hospital after travelling there for unrelated treatment.
There are currently 13 patients in the hospital, with one in intensive care.
A lockdown in Tennant Creek has been extended for two days until Wednesday at 5pm.
Ms Manison encouraged people to get vaccinated, saying the rate remained low in the town and surrounding Barkly region.
Ali Curung Indigenous community, 170km south of Tennant Creek, also remains locked down with Ms Manison saying its 44 per cent first dose rate needed to climb before restrictions would ease.
A face mask mandate in Katherine and surrounding areas has been lifted.
It comes as the NT opens its borders to travellers who are fully vaccinated and strips quarantine requirements for arrivals.
Travellers wishing to enter the the territory now have to return a negative PCR test taken within three days of their arrival.
They also need to get re-tested within three days of arriving and again on their sixth day in the NT.
Unvaccinated travellers have been barred, with only returning residents exempt.
Travellers will need to show proof they are vaccinated or evidence they are ineligible for the jab.
Tests are free at NT government coronavirus testing facilities and travellers are not required to isolate while they wait for the results.
Authorities are also handing out free rapid antigen test kits at the airport for use at home if people develop symptoms.
Arrivals must stay in high vaccination areas, such as Darwin and Alice Springs.
They are also required to download the G2G Now app and complete location check-ins when ordered.
Most travellers are banned from dozens of remote communities where vaccination rates remain below 80 per cent
Unvaccinated people who try to get into the territory will be turned away and could face a fine of more than $5000.
Those allowed in must quarantine at their own expense for 14 days.
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