A snap territory-wide lockout started at 1pm local time on Thursday as locally acquired cases surge.

"Today's escalation in case numbers is concerning," Chief Minister Michael Gunner told reporters.

"I don't like that we have over 200 cases.

"Our community transmission rate has grown in recent days".

All told, 27 new locally acquired cases were detected, up from three two days ago but down from 34 on Wednesday.

Mr Gunner said the increase was a result of New Year's Eve social gatherings with more than 50 per cent of new infections diagnosed in people aged 20 to 39.

He said the NT's virus reproduction rate had climbed to 4.5 and about 10 per cent of tests were yielding a positive result.

A territory-wide lockout of unvaccinated people aged 16 and over will run until noon on Monday when a proof of vaccination pass system will be rolled out.

It will run on the territory's check-in app and apply to most hospitality and entertainment venues

Under the lockout, unvaccinated people can only leave their homes for medical treatment and testing, essential goods and service and to care for a vulnerable person.

They are not permitted to go to workplaces or travel more than 30 kilometres.

The lockout is expected to reduce pressure on the health system amid staff shortages.

Access to vulnerable Indigenous communities has also been restricted with only residents and essential workers who show evidence of a negative rapid antigen test permitted to enter.

Asked if the NT would re-close its borders, Mr Gunner said the testing regime was catching cases and there was no clinical evidence to support the move.

Of the 256 cases, 10 are known close contacts, 112 remain under investigation and 107 are interstate and international arrivals.

Two were recorded in Tennant Creek, 510km north of Alice Springs, as the Delta outbreak that started in Darwin in late October continues to grow.

Eighteen people tested positive in Yulara, 18km from Uluru, as the virus spreads through the community of about 1000 people.

Twenty-three infected people are in NT hospitals, with eight cases suffering severe symptoms in Royal Darwin Hospital.

Two of those are in intensive care, with one on a ventilator.

The territory recorded 117 new cases on Wednesday and 75 on Tuesday.

Meanwhile, the NT will not ease testing requirements for people who return a positive rapid antigen test, and will continue to confirm the result with a PCR test.

This is despite national cabinet agreeing on Wednesday that people who record a positive result from a rapid antigen test will no longer have to get their results confirmed by a PCR.

The change was designed to help ease pressure on PCR testing sites - which have experienced surges in demand due to widespread shortages of rapid tests.

Australian Associated Press