With the Syndey coronavirus cluster continuing to grow, Australian state premiers are implementing new travel restrictions to keep the outbreak from spreading beyond New South Wales.
NSW reported 30 new cases of coronavirus today and tighter restrictions were imposed across the Greater Sydney area.
Contact tracers are following dozens of lines of inquiry and officials are poring over CCTV footage as they scramble to find the original source of the cluster.
Such is the mystery surrounding the outbreak that NSW's chief health officer has speculated that finding "Patient Zero" could be a "challenge beyond us".
In the meantime, the outbreak has led to a rapid response from Australia's other states and territories. An overview of each:
Victoria's Premier Daniel Andrews announced he is closing the border to NSW from midnight tonight.
"I must announce on the best public health advice that from 11.59pm tonight we will declare all of Greater Sydney and the Central Coast a red zone," Andrews said today.
According to Victoria's traffic light system, travellers from a "red zone" are not permitted into Victoria without 14 days in quarantine.
"If you're in Greater Sydney, stay in Greater Sydney," Andrews said.
"We are going to protect what we have built and that is why the border will be closed from midnight tonight."
The rest of Sydney is currently an "orange zone" and those travelling from there must get tested and isolate until they can produce a negative Covid-19 result.
Western Australia Premier Mark McGowan announced a hard border with NSW last night, meaning that anyone coming into WA from NSW must seek an exemption.
If successful in gaining an exemption, they must self-isolate for 14 days and be tested for Covid-19 once in Perth.
"I know the changes are going to be hard for many people... This is not an easy decision to make," McGowan said.
Prior to this week, visitors to WA from all states and territories – except from SA – could arrive without having to apply for an exemption or quarantine.
Queensland has stopped short of shutting its border to NSW, but authorities in say they are "already ready" to close the border within a single day if the premier makes the call.
All travellers from NSW will be required to fill out a border declaration form from 1am (local time) on Sunday morning.
Anyone who has been in the Northern Beaches region on or since December 11 and is already in Queensland is required to get tested and quarantine at home or in accommodation until 14 days after the date they left.
Anyone arriving in Queensland from the Northern Beaches area after 1am on December 19 will be required to go into hotel quarantine at their own expense, and get tested.
Anyone from the NSW Central Coast or Greater Sydney area will be asked to get tested upon arrival in Queensland and isolate until they receive a negative result.
Anybody who has been in the Greater Sydney area will be required to complete 14 days of quarantine on arrival in South Australia, at home or in a hotel at their own cost. There is a "hard border" against anyone from the Northern Beaches.
Health officials are contacting anyone who has arrived in the state from the Northern Beaches area in recent days, who they will direct into quarantine. Anyone who has come in from other parts of NSW will require testing.
Tasmania has declared all of Greater Sydney to be a "medium risk" area, meaning travellers must quarantine for 14 days in their home, or if they are unable to, quarantine in a hotel at their own cost.
Premier Peter Gutwein said he "made no apology" for announcing the additional restrictions.
The Northern Territory declared Sydney's Northern Beaches a coronavirus hotspot and will require residents from the area enter mandatory, supervised quarantine.
People in Canberra are advised not to travel to the northern beaches region. People in the ACT who have been there since December 11 must self-isolate and get tested.