Malcolm Turnbull warns Britain leaving the European Union will be a "very big shock".
After months of heated debate, Britons will vote in a once-in-a-generation referendum on Thursday on whether to remain within the 28-member European Union or leave.
The "leave" and "remain" campaigns are neck-and-neck in the polls.
"It would be a very big shock if Britain votes to leave the European Union," Mr Turnbull told reporters in Geelong on Thursday.
"There will be obviously great efforts to ensure that the consequences of that shock are minimised."
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However, he said the strategic implications would not be as severe - as Britain would not be leaving NATO.
Shadow assistant treasurer Andrew Leigh said a "Brexit" would lead Britain to look more inward and force it to renegotiate trade agreements with other countries.
"For Australian companies that use Britain as an entry point to the EU it would also generate disruption," Dr Leigh told AAP on Thursday.
Disruption would also flow from the labour market.
"It certainly is a campaign that would be, in my view, destabilising to the global economy."
Because Britain was a significant trading partner for Australia, more so in services than in goods, all our exporters involved in Britain would be potentially affected, Dr Leigh said.
