The boss of Qantas has apologised over this week’s cyber breach amid fears up to six million customers have had their data stolen.

The airline’s CEO, Vanessa Hudson on Friday said she recognised the data breach was a serious concern.

WATCH THE VIDEO ABOVE: Qantas CEO apologises for data breach.

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“What I would first like to say is I acknowledge the impact to all our customers and, first and foremost, I’d like to apologise to them,” Hudson told 7NEWS from Athens.

“I know the stress that it has created for many, many millions of customers that we’ve had.”

The national carrier revealed on Wednesday that a third-party platform used by one of its call centres had been targeted in a major cyber attack, resulting in the leak of personal customer details. The airline was first alerted to the hack on Monday when it detected “unusual activity” in its system.

Names, phone numbers, dates of birth and email addresses are among the information believed to have been compromised.

Qantas confirmed scammers were already impersonating the airline in the wake of the attack and warned customers to be vigilant.

Hudson confirmed that passport details, credit card information, passwords and frequent flyer accounts were not accessed.

Qantas CEO has apologised for a cyber hack that could affect millions of customers. Credit: 7NEWS

She said Qantas customers would be informed next week regarding what specific data of theirs may have been affected.

Hudson said the threat had been contained and their systems were now secure.

“We are going to learn from this. We are not going to stop in the effort to make sure that our systems going forward are as strong as possible,” she said.

Hudson was on holiday in Europe when the cyber incident came to light and has now cut her trip short to return to Australia.

The CEO did not mention any compensation when delivering the apology.

The national carrier said it was putting in extra security to restrict access to its systems.

“Qantas has notified the Australian Cyber Security Centre and the Office of the Australian Information Commissioner,” the airline said.

“Given the criminal nature of this incident, the Australian Federal Police has also been notified.

“We will continue to support these agencies as the investigation continues.”

The airline has also established a dedicated customer support line and has put a dedicated page on its website to keep customers updated.