The Northern Territory has declared Sydney a coronavirus hotspot and will keep quarantine restrictions in place for anyone arriving from the harbour city.
The move follows increasing concerns over an outbreak of COVID-19 cases in Sydney's southwest where 34 infections have been linked to the Crossroads Hotel.
Chief Minister Michael Gunner said the move follows a meeting of the Security and Emergency Management Committee on Wednesday.
"We will declare all 30 local government areas in greater metropolitan Sydney as hotspot areas for the purposes of travel to the Northern Territory," Mr Gunner said.
"This means that from Friday, if there are any arrivals to the Territory from Sydney, or who have been in Sydney in the previous 14 days, they will be directed into mandatory, supervised quarantine and charged $2500."
Similar arrangements are also in place for travellers from Victoria with anyone arriving from those regions to face 14 days' quarantine at their own expense.
However, the NT will lift border restrictions for people from other states on Friday.
Mr Gunner said the Territory's decision was not just based on the current situations in Victoria and Sydney, but on how bad things could get.
"This situation in Sydney has the potential to get worse before it gets better and we need to assume that it will get worse," he said.
"To open our borders to Sydney right now, when we don't know the full extent of this cluster, would be a roll of the dice.
"And I don't gamble with the lives of Territorians."
The Territory will review its Sydney hotspot declaration in two weeks but Mr Gunner said he did not expect the restrictions to be in place for as long as those for Victoria.
"But I will not make any promises about a date," he said.
So far, 34 cases have been linked to the Crossroads Hotel in Casula, in Sydney's west, at least 20 of them patrons.
Victoria has recorded 238 new cases on Wednesday and an additional death in the current outbreak.
NT Chief Health Officer Hugh Heggie said travellers continued to present the biggest risk to the Territory.
He said Sydney and Victoria were being monitored and the NT's response was proportionate in the circumstances.
The NT government has also vowed to keep a police presence at all borders for the foreseeable future, regardless of moves to ease border measures for most states.
Australian Associated Press