Optus says it has finally restored internet and phone services to the millions of customers who were hit by today's 13-and-a-half-hour network outage.
The telco said it had started pushing out a fix at around lunchtime, but it wasn't until after 5.30pm that the issue had fully been resolved.
"Optus sincerely apologises to customers for today's outage," a spokesperson said.
READ MORE: Can you get compensation for the massive Optus outage?
"We know that customers rely on our services, which is why the whole team at Optus has been working hard to fix this.
"Services have now been restored, and customers should now be able to be back online.
"We again thank customers for their patience."
The outage led to about $2 billion being wiped from the company's value as its share price crashed around 4.5 per cent over the course of the day.
Earlier, Optus CEO Kelly Bayer Rosmarin said the telco has "no line of sight" into the root cause of the outage that knocked the network out this morning, but that a fix is on the way.
The issues preventing Optus customers from making calls and accessing mobile data began at about 4am.
READ MORE: All the services impacted by the Optus outage
Asked about compensation for users, Bayer Rosmarin said Optus would look into that as soon as services were up and running again.
She said on several occasions that she was "very, very sorry" for the outage.
Optus mobile customers reported their phones showing SOS on the signal indicator, which is a sign that your regular network is down, but that they were still able to access alternate networks in the event of an emergency call.
Communications Minister Michelle Rowland said Triple Zero had confirmed that fallback, known as "camping", was working this morning, but she said Optus landlines did not have access to the same technology.
Compounding matters, the telco said it had received reports of mobile customers having issues contacting the emergency number.
READ MORE: When will the Optus outage be fixed? What we know
The outage originated from a "deep fault" within the network, but the specific cause remains a mystery.
Rowland said there was no indication the outage was due to a cyberattack, a position the Department of Home Affairs also took earlier.
The government will continue to work with telcos to ensure access to emergency lines stays open for Australians, she said.
A number of government state and federal agencies were monitored for how the outage affected them, but Rowland didn't specify which ones.
However, it's been revealed that Australians had been unable to contact either the ATO or the Department of Home Affairs due to the outage, according to 2GB's Chris O'Keefe.
READ MORE: When the Optus boss is forced to use WhatsApp to talk, you know it's bad
Rowland said it was too soon to consider the issue of potential reparations for affected customers.
But she urged small businesses to "keep receipts" during the time they were affected.
Linked networks such as Dodo and Amaysim were also affected.
Commonwealth Bank also warned customers had been experiencing difficulties in contacting or receiving messages from the bank, including NetCode messages.
"If you need to contact us, you can still message us through the CommBank app, but there may be delays," the bank said earlier today online.
"Our other services including ATMs, NetBank, CommBank app, CommBiz and merchant terminals are also still available. We apologise for the inconvenience."
'Deep and significant problem'
Rowland earlier told 2GB radio Optus faced a "deep and significant problem".
"The understanding I have at this time is it is affecting both broadband and mobile services," she said.
She said it had been a "very frustrating morning" for many around the country, and urged Optus to keep the public updated.
Today tech expert Trevor Long, who also contributed to this story, said the "knock-on" effect of the outage could make this morning's outage the biggest in recent memory.
"Businesses that rely on Optus for payments and communication, they will be crippled this morning," he told Today.
"And this is without question the biggest telco outage we have ever seen because it spans both home Wi-Fi and broadband."
In the hours after the outage, Optus messaged concerned customers.
"We apologise for any inconvenience caused while we have the issue resolved," it said.
OPTUS OUTAGE: What we know so far
- The network outage was first reported at 4.05am, and was reportedly caused by a "deep fault" in Optus' network.
- Up to 10 million people were affected, alongside businesses, hospitals and banks.
- Landline customers are unable to call triple zero (000), but mobile users can reach the emergency line.
- As of 5.35pm, Optus said services have been restored for its customers.