Emergency calls made to Triple Zero from Optus mobiles won't be affected by the current Optus outage - but landlines will - as millions of Australians around the country continue to go without mobile data and network access.
Even people who aren't Optus customers are affected, with institutions including banks, hospitals and more experiencing difficulties.
Here's a round-up of what's been affected, and what they've had to say.
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Optus
"We're aware of an issue impacting Optus mobile and nbn services and are working to restore services as quickly as possible.
"We understand connectivity is important and apologise for any inconvenience caused.
"Our teams are working urgently to restore services. We will provide updates as soon as possible. We apologise sincerely to our customers."
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Triple Zero
Calls to Triple Zero can still be made, including from Optus mobile phones displaying the "SOS" symbol.
Optus landlines, however, cannot make Triple Zero calls.
NSW and South Australia police have both confirmed Triple Zero lines are unaffected.
However, people are reminded only to call if they are in need of urgent assistance during an emergency.
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Commonwealth Bank
"Due to the ongoing Optus outage our call centres are unable to receive calls.
"Our ATMs, NetBank, CommBank app, branches, CommBiz and merchant terminals are still available.
"You can still get in touch via the CommBank app or online banking, but there may be delays."
ANZ
"We are aware of the the current nationwide Optus outage and that this may be affecting customers trying to contact us.
"We apologise for any inconvenience.
"The ANZ App, ANZ Plus app, ANZ Internet Banking, Message Us and ATMs continue to be available during this time."
Westpac
"The current Optus outage means we are unable to take some calls at this time.
"Our branches, chat, mobile and internet banking services are still up and running.
"We will keep you updated (on X)."
NSW Health
"NSW Health is aware of impacts on some NSW Health telephone and internet services as a result of today's Optus outage.
"NSW Health continues to investigate the situation and is taking steps to minimise disruption to services where required.
"Maintaining patient care and safety remains our highest priority."
Service NSW
"Due to the national Optus outage people are unable to contact Service NSW Contact Centres on 13 77 88.
"Customers can continue to transact in person at Service Centres or via the website at www.service.nsw.gov.au if their internet provider is unaffected by the outage.
"We apologise for any inconvenience caused."
St George
"The current Optus outage means we are unable to take some calls at this time.
"Our branches, chat, mobile and internet banking services are still up and running.
"We will keep you updated (on X)."
Ramsay Health Care
"Ramsay hospital phone services are being impacted by a national outage of Optus telecommunications.
"At this time, we are unaware how long this outage will continue.
"If you need to contact your local Ramsay hospital, please direct inquiries via the contact form on the local hospital's website.
"Thank you for your patience and understanding."
Sydney Airport
A spokesperson said operations are running as usual this morning.
There is extra load on the wi-fi, but passengers are accessing their online tickets and checking-in without issue.
Northern Health, Melbourne
"All phone lines into Northern Health campuses are currently being affected by an Optus outage.
"This includes phone lines into Northern Hospital Epping, Broadmeadows Hospital, Bundoora Centre, Craigieburn Centre, Kilmore District Hospital, and Victorian Virtual Emergency Department (VVED).
"We apologise for any inconvenience."
