Emergency calls and mental health hotlines felt the brunt, while hospital networks appeared to adapt quickly.
Emergency calls and mental health hotlines appear to be the hardest-hit health services as Optus continues to battle to restore its functionality in NSW, Victoria and Queensland.
It remains unclear how long it will take to restore the whole network which suffered a major outage from about 4am AEST.
Optus tweeted about 1pm that work was under way to resolve the outage, estimated to have affected 10 million customers nationwide, but connection would remain staggered over the next few hours.
However, a spokesperson for the company confirmed that there were ongoing issues with calls to emergency services, with Optus landlines and some mobile phones unable to make triple-zero calls.
Customers needing to contact emergency services were advised to use a mobile line to call 000, with the call redirecting to another carrier if available, or to find another device, the telecommunications giant said.
According to Optus CEO Kelly Bayer Rosmarin, the outage was first identified at around 4am today.
While the cause of the outage remains uncertain, Ms Bayer Rosmarin confirmed that there was as yet, no evidence it was the result of a cyberattack or software malfunction.
âIt is highly unlikely [to be software-related]. Our systems are actually very stable, we provide great coverage to our customers, this is a very rare occurrence,â Ms Bayer Bayer Rosmarin told ABC radio.
âWhen I have more information about the root cause, I will be the first to let our customers know.â
Mental health and crisis support providers across the country reported disruptions to their mobile phone services as a result of the outage, with Mind Health PHN and MensLine Australia advising callers to expect delays and to redirect their call to Lifeline if urgent.
TMR approached Lifeline for comment but did not receive a response before deadline.
Hospitals across the country also reported disruptions to their phone lines, with many unable to receive incoming phone calls and some unable to make external calls as a result of the outage.
In Victoria, Eastern Health, Western Health and Calvary Health all recorded disruptions to their services, with Eastern Healthâs incoming and outgoing phone lines down and some residential aged care homes operated by Calvary Health unable to receive calls.
However, Royal Melbourne Health, Alfred Health and Monash Health told TMR that their services had not been impacted by the outage.
The outage affected phone lines for Ramsay Health Care, which operates three Sydney private hospitals â St George, North Shore and Westmead â and told its customers to use online contact forms.
According to a spokesperson for Queensland Health, the state had largely escaped unscathed as the majority of hospitals were connected to Telstraâs telecommunications network.
âTelstra is the primary telecommunications provider for Queensland hospitals, and services are operating and able to support consumers,â the spokesperson said.
âPatient safety is paramount for Queensland Health and there are well-established business continuity plans in place to ensure minimal clinical impacts in cases such as this.â
Canberra Health Services told TMR that all of its facilities had been impacted by the outage, including the Canberra Hospital Switch Board, Maternity Assessment Unit and Access Mental Health Services, with the exception of North Canberra Hospital which ran on Telstra.
âCanberra Health Services advises the community to call 000 in an emergency or attend the facility for the service need or scheduled appointment,â a spokesperson for Canberra Health Services said.
âNo health services have been cancelled and business continuity plans have been enacted and are working well.â
According to a statement released by NSW Health, the department was investigating affected telephone and internet services across the state and taking steps to mitigate any delays.
âNSW Health is aware of impacts on some NSW Health telephone and internet services as a result of todayâs Optus outage,â a spokesperson for the department said.
âNSW Health continues to investigate the situation and is taking steps to minimise disruption to services where required.â
Nepean Blue Moutains LHD confirmed that its mobile and networking services were largely unaffected as they ran on other networks.
Federal Communications Minister Michelle Rowland confirmed she had been in touch with Optus.
âI urge Optus to utilise other mechanisms, including broadcasting radio and television, to get these messages out. Because ⌠people are asking me questions. Theyâre very anxious,â she told the ABCâs RN Breakfast.
âI think as long as people know that something is happening, that people are on the job, and they have some expectations, then I think that will allay some concerns that are there right now.â
Shadow Communications Minister David Coleman also called on the telco to communicate with customers.
âThe Optus outage is impacting millions of Australians and businesses,â he said. âGovernment should provide any assistance needed to get this issue resolved as soon as possible.â