The personal data of more than 300,000 Australian Facebook users was “improperly shared” with an analytics firm as part of the recent data harvesting scandal, the social media giant has revealed.

It comes as the Australian Privacy and Information Commissioner officially launched an investigation into the data harvesting and whether Facebook has breached privacy laws.

In a statement on Wednesday, Facebook revealed that the data of about 80 million users had been harvested through a personality quiz app on the site and shared with data analytics company Cambridge Analytica. This is a significant increase from the 50 million users figure originally reported last month.

Facebook also confirmed that an estimated 311,127 Australians were impacted by the data harvesting scandal.

The majority of users impacted by the scandal were from the US. The data was then reportedly used by Cambridge Analytica to influence the result of the 2016 US presidential election, along with other major events.

Following from Facebook’s confirmation that hundreds of thousands of Australians were impacted, acting Privacy and Information Commissioner Angelene Falk confirmed that her office has launched an investigation.

“Today I have opened a formal investigation into Facebook, following confirmation from Facebook that the information of over 300,000 Australian users may have been acquired and used without authorisation,” Ms Falk said in a statement.

“The investigation will consider whether Facebook has breached the Privacy Act. Given the global nature of this matter, the OAIC will confer with regulatory authorities internationally.”

It’s the first time that Facebook has admitted to the scale of the data scandal that has engulfed the tech giant over the last week.

In the statement, Facebook admitted that it may not ever know the exact amount of users that were impacted.

“Using as expansive a methodology as possible, this is our best estimate of the maximum number of unique accounts that directly installed the thisisyourdigitallife app as well as those whose data may have been shared with the app by their friends,” the company said.

Only 270,00 users actually installed the app, but these users also shared the data of all of their Facebook friends with the researcher. Facebook says that this researcher then broke its rules by handing over this data to Cambridge Analytica.

Cambridge Analytica has denied these claims, saying in a statement that it had received the data of only 30 million people, and this was deleted after it was told by Facebook that it had been “improperly obtained”.

Impacted Facebook users will be notified by a message at the top of their NewsFeeds from next week. Facebook CEO Mark Zuckerberg admitted the company had made a “huge mistake”.

“We didn’t take a broad enough view of what our responsibility is, and that was a huge mistake,” Zuckerberg said during a press call. “It was my mistake.”

He admitted that it was the company’s responsibility to protect its users’ data.

“It’s not enough to have rules requiring they protect information, it’s not enough to believe them when they tell us they’re protecting information - we actually have to ensure that everyone in our ecosystem protects people’s information,” Zuckerberg said.

Facebook also admitted that most of its users “could have had their public profile scraped” by various third parties, without their knowledge. It said that a now-disabled feature where users could be searched by their email addresses and phone numbers was being used by third parties to harvest data.