"Keeping customers connected is our priority and we apologise for any inconvenience caused," the spokesperson said.

Internet and mobile services were hit by the problem mid-morning Friday.

People who tried to make calls were met with the following message: "Due to temporary service difficulties we are unable to connect your call during this time."

The Downdector service showed spikes in outage reports in Sydney and Brisbane about 11am Friday, as well as Melbourne and Canberra.

It took hours for the 4G and 5G services to be restored and late Friday, Optus said its 3G customers continued to "experience service issues".

That was sorted by late Saturday morning, an Optus spokesperson said.