Prime Minister Scott Morrison says a Russian invasion of Ukraine is "imminent" and reapplied pressure on China to denounce violent actions in eastern Europe.
Mr Morrison said he hoped conflict would not occur but says "what we are seeing leads us to fear the worst".
"It's important for all nations to denounce the threats of terrible violence that Russia is making against Ukraine," he said.
"It remains a highly volatile situation and an invasion of Ukraine is, of course, imminent."
The comments came hours after Defence Minister Peter Dutton indicated Ukraine was on the cusp of an "all-out conflict".
Mr Dutton told the Nine Network on Friday there had been multiple signs an attack would happen soon.
"It's tragic and we'll see terrible scenes unfolding," he said.
"You would expect that President (Vladimir) Putin, who obviously can't be taken at his word, is manufacturing some sort of trigger, or is in the process of executing the final stages of his plan to go into Ukraine."
US President Joe Biden said Moscow was preparing a pretext to justify an invasion and there was "every indication" Russia would attack.
"We have reason to believe they are engaged in a false-flag operation to have an excuse to go in," Mr Biden.
The White House says Russia added 7000 more troops to the border in the past 24 hours, and while the total number remains unclear, NATO member Estonia estimated it around 170,000.
President Putin has accused the US of stoking tensions, as Ukrainian forces and pro-Moscow rebels traded fire in Ukraine's east.
Mr Dutton said while European leaders have attempted to prevent a conflict in Ukraine, President Putin was intent on military action.
"That really is going to result in the loss of innocent life," he said.
"We've seen it before in eastern Europe. We don't want it repeated but we live in a very uncertain world."
The head of Ukraine's diplomatic mission in Australia, Volodymyr Shalkivskyi, said even if an invasion didn't take place, the effect on the nation would be detrimental.
"Two, three or five months of such pressure will be devastating for our economy," he told the Australian Strategic Policy Institute.
"It's my personal opinion that Mr Putin has enough resources to wait for months, for years, keeping pressure on Ukraine and waiting for the perfect timing."
Despite the pressure from Russia, Mr Shalkivskyi said Ukraine should still join NATO.
However, countries like Australia pulling diplomats out of Ukraine had sent the wrong message.
"We respect this decision by the United States and other countries that followed suit," he said.
"We facilitated this decision for a relocation to be as smooth as possible, but we don't believe it was necessary."
Labor deputy leader Richard Marles said the warning from the defence minister was dire.
"We all hope for that 11th-hour miracle. What's really important is that the international community is of one, giving support to Ukraine," he told the Nine Network.
"Russia should be withdrawing, obviously, and de-escalating but it's really important at this moment that the world stands with Ukraine."
