Online services are being restored following a widespread outage that affected ANZ, Westpac and the Commonwealth Bank (CBA), as well as other businesses such as Virgin Australia and Australia Post.
On Thursday afternoon, customers took to social media to report troubles accessing bank services online or through banking apps.
National Australia Bank was the only one of the big four banks not to experience any disruption, along with many of the smaller banks and credit unions.
However, the problems went far deeper, with staff at some of the major banks unable to access the internet and the Reserve Bank's website and other systems also down for a period of time.
"We have implemented appropriate mitigations and the website is now back up and running," the Reserve Bank of Australia said.
However, the ABC understands some market operations between the Reserve Bank and commercial banks were cancelled today because of the technical problems many of the participants were facing.
However, it is understood that end of day financial settlements between the major banks were carried out as usual.
Companies took to social media to inform their customers of the problem, even as they themselves were scrambling to figure out what had gone wrong.
"We're aware some of you are experiencing difficulties accessing our services and we're urgently investigating," CBA wrote on Twitter.
Virgin Australia tweeted that it was experiencing a system outage that was impacting its website and contact centre.
Australia Post was also affected, describing the issue as an "external outage" affecting a number of its services.
By 4pm (AEST), services were starting to be restored, with some bank customers able to log in to their apps.
Shortly after 5pm, Virgin confirmed it was back up and running.
"Virgin Australia is pleased to confirm that an IT outage has been resolved and our website and guest contact centres are operating as usual," the airline said in a statement.
"Flights are largely operating as scheduled and we apologise to any guest who has been inconvenienced."
Akamai blamed for outage
The source of the problem was an outage with service provider Akamai.
Virgin Australia confirmed it "was one of many organisations to experience an outage with the Akamai content delivery system today and we are working with them to ensure that necessary measures are taken to prevent these outages from reoccurring".
Akamai is a US-based global content delivery network (CDN), cybersecurity and cloud service provider.
The company promotes itself as "the world's largest and most sophisticated edge platform" to protect platforms and users from online threats while delivering content quickly.
The ABC has approached multiple Akamai representatives for comment.
An outage at a different CDN, Fastly, was behind the recent shutdown of major global news and media sites, including the BBC, Financial Times and Reddit.