The government and institutions of Australia are being targeted by an ongoing sophisticated state-based cyber hack, according to Prime Minister Scott Morrison.
Morrison said the cyber attacks were widespread, covering "all levels of government" as well as essential service providers and businesses.
He declined to identify a specific state actor, adding no major personal data breaches had been made.
The activity has been increasing in frequency over many months, he said.
He said cyber experts had identified it as a state hack "because of the scale and nature of the targeting and the trade craft used".
When asked whether that country had been identified, Morrison said he would not make "any public attribution".
"There are not a large number of state-based actors that can engage in this type of activity," he told reporters on Friday.
He stressed that similar "malicious" activity had been seen in jurisdictions globally, making it not unique to Australia.
Cyber intelligence experts have long linked various hacks in Australia to China.
They say China is one of the few states, along with Russia, Iran, and North Korea, which have the capacity for such attacks - and are not allied with Australia.
"There's always simmering tensions between Russia and China so really it comes down to those being the key actors they [Australia] would be referring to," expert Joshua Kennedy-White said in this light.