The Australian Taxation Office is continuing to struggle with the fallout of a storage collapse that has caused massive technical issues since December, with all its online services offline since Thursday morning.
Customers attempting to access the ato.gov.au site are met with an "unknown error" message and a notice to contact the ATO technical team.
The tax office confirmed all its online services were offline and said it was investigating the issue "as a priority".
It revealed the cause was related to the collapse of an HPE SAN network in early December last year.
"We are replacing the affected hardware, but this process will take some time," it said in a statement.
"Unfortunately, these issues are impacting services including the tax agent, business and BAS portals, ATO online, the Australian Business Register (ABR), Standard Business Reporting (SBR), and superannuation online services."
The agency said it had directed all available resources to resolve the outage.
Update 4:43pm: The ATO said its systems would not be back online today.
"Unfortunately we are continuing to experience issues with the systems impacted by this morning’s outage," it said.
"We are working to resolve these issues as a priority, and will continue to keep the community informed of our progress. We will issue a further update tomorrow morning.
"We apologise for the inconvenience this is causing."
Update 3/2/17 9:30am: The agency said ATO and HPE technicians had made "significant progress" on restoration of services, but the process was "highly complex".
"Work will continue around the clock with an immediate focus on restoring priority services," it said.
"The performance of different systems may vary as this restoration process is undertaken.
"Thank you for your continued patience during this time."
The collapse of the storage network on December 12 - which downed its entire online presence and several internal systems for two days, and was followed by a second outage the following week - is being investigated by PwC as part of an independent review into what went wrong.
The review will be finalised in March, and runs alongside the ATO's own internal investigation into the matter.