The Northern Territory will open its borders from Friday but not to Sydney and Victoria.
Chief Minister Michael Gunner today announced Sydney would be added to the whole of Victoria as coronavirus "hot spots" which would not be part of the opening.
He said there was now a large cluster of cases in Sydney.
"It is possibly heading up to Queensland already."
The Sydney decision would be reviewed in a fortnight, he said.
Mr Gunner said police would maintain the hard border crossings into the NT "indefinitely".
He said any arrivals from the hot spots would be directed to mandatory quarantine at Howard Springs and have to pay $2500.
He admitted being "stressed and anxious" about the Friday border opening given the NT was largely virus-free.
"We have to get back into the habit, it has to be a life habit, of washing hands, social distancing," he said.
Mr Gunner said personal behaviour was the most important measure for the Territory to keep the virus under control.
There will be limited exemptions to the border restrictions for Melbourne and Sydney in regards to freight.
Both cities host major distribution centres for food and other supplies which still need to keep flowing through to the NT, officials said.
"The worst thing we can do is welcome coronavirus and not a visitor," Mr Gunner said.
"Please reconsider any travel outside the Territory at the moment, it is not worth the gamble."
"We need to get back in the habit, help us stop the spread."
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