Up to 50,000 iiNet customers were cut off from the Internet last night after field workers bungled the network's cabling.
The outage occurred in the Sydney suburb of Cronulla and spread quickly to surrounding areas after a cable was plugged into the wrong port at 9pm.
iiNet chief technical officer, Greg Bader, said some 15,000 customers were cut-off until about 11.30pm, while most subscribers were back online "soon after" the incident.
The network was largely operational by 2.36am, according to an update to customers from the ISP, which said any follow-on issues were being corrected.
"A fair chunk of Sydney was out. It was a significant outage," Bader said. "About 50,000 customers bounced, and not all came back.
"Services are working properly and I'm finding out the details of what happened."
Network management company Remote Hands was responsible for the incident.
It follows a Telstra Next G network outage in Queensland which cut of voice and data services following a network upgrade in May.
A Telstra DNS upgrade was fingered for a Bigpond outage in September.
Twitter was flooded with complaints about a power outage at Equinix's Sydney data centre which apparently knocked out data and network systems, including VoIP last year.