Foreign Minister Julie Bishop has warned of further global market volatility if Britain exits the European Union.
Two days before the polls close in the so-called Brexit referendum, a number of high-profile figures have warned of financial risks and national security concerns if the "yes" vote succeeds.
Ms Bishop said it was a decision for the British people, but a Brexit would not be in Australia's national interest.
The European Union was a significant trading bloc security partner for Australia.
"Having a like-minded, indispensable friend like Britain within the European Union would give that region strength and stability," Ms Bishop told the National Press Club in Canberra on Tuesday.
If Britain exited the EU "there will obviously be a period of time as Britain negotiates the terms of its withdrawal from the EU".
"Our concern is that that will lead to considerable instability," she said.
"The financial markets have already shown a level of volatility just at the mere prospect of Britain withdrawing - so we could expect more of that."
If the Brexit went ahead, Australia would seek to "re-engage" with the EU and Britain once the terms of the exit were released, Ms Bishop said.
Labor foreign affairs spokeswoman Tanya Plibersek declined to comment, saying a Shorten government would work with whatever the UK people decide.
