NT Health Minister Natasha Fyles said the girl from Katherine had seven close contacts and turned out to have the virus when she went to the hospital for treatment yesterday.
Ms Fyles said the child is believed to be in the later stages of having the virus and took the local coronavirus cluster to 61 cases.
The health minister said the case would mean Greater Katherine’s lockout would have to be extended by a further 24 hours.
It was supposed to end at 12 o’clock tomorrow, but instead ends at 12 o’clock on Wednesday.
Ms Fyles further announced that the Binjari community could go from lockdown to lockout due to the lack of new cases in the city.
She said one of the other new cases of COVID-19 recorded overnight was a close contact with a traveler who arrived from Melbourne last week and who had been in quarantine throughout their infectious period.
The second case is a 60-year-old woman who arrived by plane from London on 29 November.
She has been in home quarantine since her arrival.