Hackers have threatened to leak the stolen health data of 1,000 famous Australians in a cybersecurity incident described by the government on Thursday as a "huge wake-up call."

Medibank, one of Australia's largest private health insurers, said on Thursday that the hackers were claiming to have stolen 200 gigabytes of data. 

"The criminal has provided a sample of records for 100 policies," it said in a statement to the Australian stock market.

"This claims data includes the location of where a customer received medical services, and codes relating to their diagnosis and procedures."

The insurer announced a trading halt as details of the hack emerged on Wednesday morning. 

The hackers threatened to leak or sell the data, starting with 1,000 high-profile Australians, unless Medibank paid a ransom.

The personal information of some 9 million Australians - almost a third of the population - was exposed in September in a hack targeting telecoms company Optus. 

The Optus hack was one of largest data breaches in Australian history.

Home Affairs Minister Clare O'Neil said on Thursday that cybersecurity could no longer be taken for granted.

"Combined with Optus, this is a huge wake-up call for the country," she told ABC Radio. 

"This is the new world that we live in. We are going to be under relentless cyberattack, essentially from here on in."