The Northern Territory has declared parts of Western Australia COVID-19 hotspots and revoked restrictions on Sydney's western suburbs.
Perth, and WA's Peel region and South West were added to the hotpot list after the areas went into a five-day lockdown amid fears an infected quarantine facility security guard may have spread the virus.
"Anyone who arrives in the Territory from Perth ... will be directed to mandatory supervised quarantine," Chief Minister Michael Gunner told reporters on Monday.
About 2000 people who arrived in the Top End from Monday last week have been directed to isolate and get tested for coronavirus until they receive a negative result.
"Given how infectious these new strains are and that we don't yet have a complete picture it's best to go early and go hard until we know more," Mr Gunner said.
NT Chief Health Officer Hugh Heggie said it shows the virus has not gone away and the risk of it spreading in the community remains.
"This another example of international exposure to Australian and the NT. We saw it in hotel quarantine in Brisbane some weeks ago and there are various similarities here," he said.
"We've got to wait and see who has been infected if anybody by the worker. It is not clear how he acquired the infection."
He asked people who were already in the NT and waiting to be tested to be patient and stay in isolation until health workers could get to them.
The new health restrictions for travellers from WA come as the NT revokes the last NSW hotspot following a virus outbreak in the city just before Christmas.
Dr Heggie said there has been no cases reported in Sydney's western suburbs in the past 14 days and restrictions would be lifted.
People who have been in nine local government areas will longer have to quarantine upon arrival in the NT and those currently in isolation can now leave.
This includes people who have been in Blacktown, Canada Bay, Canterbury-Bankstown, Fairfield, Parramatta, Cumberland, Burwood and Strathfield.
