People who enter the Australian state of New South Wales from neighbouring Victoria will have to go into mandatory hotel quarantine from Friday.
The new measures have been introduced due to rising coronavirus infections being reported in Victoria.
Visitors will need to remain at a hotel for 14 days at their own expense.
All returning New South Wales residents, unless they live within the state’s border regions, will only be allowed to return via Sydney Airport.
Victoria has been reporting record rates of new infections despite being four weeks into lockdown.
New South Wales Health Minister Brad Hazzard said Victoria’s spike in coronavirus case numbers sent a clear message New South Wales needed to be on high alert.
Queensland, for its part, is imposing restrictions on travellers from New South Wales 24 hours later.
Queensland Premier Annastacia Palaszczuk described the closure as “a life and death situation”.
Meanwhile, a job protection scheme, JobKeeper, will be relaxed in Australia to allow more people to access it.
Treasurer Josh Frydenberg said Covid-19 lockdowns in Victoria lockdown have forced the additional $15 billion (£8 billion) spend.
Australia has recorded 255 coronavirus deaths, faring better than many countries due to effective suppression measures early in the pandemic.
But since June – when most Australians emerged from a first lockdown – the outbreak in Melbourne has spiralled.
Infections in Melbourne over the past month make up more than half of Australia’s total cases since the pandemic began.