Chief Minister Michael Gunner said.the third case, a 21-year-old Cairns woman who flew into the Territory on October 29 and subsequently tested positive for COVID, lied to officials about being in Melbourne - where she mostly likely caught the virus - before travelling to the Top End.

There have been no further COVID cases overnight and wastewater results in Katherine up until November 3 have been negative for the virus.

Katherine and Darwin are expected to remain in lockout until 11:59pm on November 8 - an extension of a day - to give for more time for contact tracing and testing work. It may be extended further if more exposure sites are found.

"The cluster remains at three cases and the Northern Territory remains community transmission free," he said.

"Case three lied on her border entry form and has been issued an infringement notice following five hours of interviews with detectives over the past 24 hours.

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"We know that before arriving in Darwin she spent time in Melbourne, which is almost certainly where she contracted the virus."

He said the case flew from Queensland to Adelaide, drove to Victoria where she spent four days then returned to Adelaide before flying back to Cairns and then onto Darwin.

"These actions have put the Territory at risk," Mr Gunner said.

"They forced Katherine into lockdown and forced Katherine businesses to shut."

Mr Gunner said that while the woman had compassionate reasons for visiting Victoria, there were not compassionate reasons for lying and coming to the Territory after visiting a hotspot.

He said she would be fined $5,024 and would also be expected to pay $2500 for her stay at Howard Springs.

"I said it before and I'll say it again. Don't lie. Don't be selfish. Think about us," Mr Gunner said.

"She'll pay because she lied to officials."

Mr Gunner said the RAAF Tindal contractor - "the index case, not our case of origin" - did the right thing because he got a test as soon as he had symptoms and allowed the outbreak to be run down quickly.

"His actions have saved lives", he said.

"His next job is to get vaccinated."

The extension of the lockout will give officials time to "keep smashing through our contact tracing and testing today in Katherine" and to check an expanded exposure site list in Darwin.

NT Health contact tracers have identified 123 close contacts, of which 119 have been contacted and are currently isolating. The vast majority of close contacts have been tested with more than 100 negative tests returned so far. Further results were expected today.

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"We've done over 500 tests - and Katherine is where the lockdown started - which is great there are no new positives," Mr Gunner said.

Schools will re-open in Katherine tomorrow, but unvaccinated parents have been asked not to go onto school grounds when dropping off children.

Additional exposure sites were added today including Jetstar flight JQ920 on October 29, with police working to track down people who were on the flight. Territory officials were also liaising with Queensland and South Australian officials on the Cairns woman's movements.

Monsoon's club in Darwin was also upgraded from a place of concern to an exposure site from 10pm on October 29 to 1.30am the following morning and on October 31 from 7.30pm to 8pm.

Mr Gunner said that there were 2600 tests completed on Saturday, all of which were negative.

"Thank you to everybody who came out and got tested. That gives us great confidence," Mr Gunner said.

Acting Chief Health Officer Charles Pain urged people to remain hyper vigilant for signs of the virus and to get tested quickly at the slightly symptoms.

Under a lockout, fully vaccinated residents are able to live normally within the lockout area. Everyone must wear a mask outside their place of residence. Travel is permitted between the Katherine and Greater Darwin lockout zones - if you are double vaccinated - but not to other parts of the NT.

Unvaccinated, including those people who have received only their first dose of a COVID-19 vaccine, must stay at home during a lockout period and are only permitted to leave for the following five reasons:

1. Medical treatment, including getting a COVID test or getting vaccinated;

2. For essential goods and services, like groceries and medicines;

3. For work that is considered essential and can't be done at home;

4. For one hour of exercise a day, with one other person or the people that you live with, and no further than five kilometres from your home; and finally

5. To provide care and support to a family member or person who cannot support themselves. This includes separated families sharing the care of children.

Vaccinated and unvaccinated essential workers are allowed to go to work in Katherine and Darwin.

It is important that you continue to use The Territory Check-In App to check in everywhere you go, every time, no matter how long you spend at that location. Checking in with The Territory Check-In App is fast and secure and allows our health teams to quickly undertake contact tracing.

Check exposure sites on the NT Health website

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