The US is now advising citizens not to travel to Australia "due to Covid-19-related travel restrictions".
Australia, as well as 21 other countries, were added to the Level 4 travel advisory list on Tuesday.
The Level 4 travel warning is the "highest advisory level due to greater likelihood of life-threatening risks" according to the US Department of State.
In the warning about Australia, The Centers for Disease Control and Prevention said "avoid travel to Australia. If you must travel to Australia, make sure you are fully vaccinated before travel."
"Because of the current situation in Australia, even fully vaccinated travellers may be at risk for getting and spreading COVID-19 variants," the CDC warning said.
The announcement has been made as Australia has started recording one of the highest Covid-19 rates per population, sitting just behind France.