Canberra hospitals, public schools and emergency services were left unable to make or receive phone calls, after a nationwide outage took down the Optus network.
Special Minister of State Chris Steel said he was not aware of any healthcare appointments being cancelled and stressed most government services were operating as normal.
"It's incredibly disappointing that this has occurred. We're seeking urgent information from Optus about how long this outage will last for," Mr Steel said.
"We'll of course keep the Canberra community updated as much as we can. But ultimately it is up to Optus to provide information to the public about when this will be restored."
An ACT government spokeswoman said government phone lines were working again from about 3.30pm.
An Optus spokesperson had said "some services across fixed [landline] and mobile are now gradually being restored" at 1pm on November 8.
"This may take a few hours for all services to recover and different services may restore at different sites over that time."
The telecommunications provider does not know the root cause of the outage but federal communications minister Michelle Rowland said the fault was likely "deep in the core" and "fundamental to the network".
Services relying on Optus are also suffering network issues including Aussie Broadband, Dodo and Amaysim.
In the ACT, trucks have been turned away from waste transfer stations, where the outage has affected weighbridges and payments.
Parents and carers needing to make emergency contact with public schools have been told to send an email.
Emergency triple-zero calls can still be placed in the ACT. Optus landline customers may be unable to make emergency calls, but Optus mobile phones can still make emergency calls using the SOS network.
The Emergency Services Agency said its flood and storm assistance line (132 500) was functional, but Mr Steel said non-emergency enquiries should be sent by email to esahaveyoursay@act.gov.au
Customers began experiencing problems with the Optus network about 4am on Wednesday.
Optus said shortly after 1pm some landline and mobile phone services were now gradually being restored across its network.
"This may take a few hours for all services to recover and different services may restore at different sites over that time," a spokesperson for the company said.
The ACT's cabinet was briefed on the issue on Wednesday morning, and Mr Steel said there would be further meetings with the Commonwealth government in the afternoon.
Mr Steel said most public Canberra health services had been affected by the outage, but phones were still operational at North Canberra Hospital, which uses the Telstra network.
"I'm advised that no health services have been cancelled and that business continuity plans have been enacted and are working well," he said.
Patients should still turn up to their scheduled appointments, he said.
The government's NXTBUS system, which provides real-time public transport network updates, was down, along with Transport Canberra's call centre. The government recommended people check online or hard copy timetables for travel information.
Mr Steel said Canberrans should delay visiting tips to dispose of waste until the Optus outage issue is fixed.
A number of traffic monitoring cameras at intersections were down, but the government said there was no significant impact to traffic flow in the capital.
Mr Steel said the ACT government was currently working through a procurement process for telephony services. He said it was "unfortunate" that during the outage most ACT government telephone lines relied on the Optus network.
"It's, generally speaking, a requirement in any procurement process that the ACT government undertakes that we assess past performance when assessing future contracts," he said.
