Rodents and a contracter have brought down many internet and phone services for the lower South Island, after the two main fibre cables supplying the area were severed on the same day.
One New Zealand has confirmed rodents chewed through a fibre cable near Dunedin, while the area's second main cable - a back up - was accidentally cut by a contractor, between Gore and Balclutha.
Hundreds of people reported internet or phone outages across Southland and Otago on Wednesday.
The website Downdetector found spikes in reports for internet outages across One New Zealand, Spark, 2degrees and Slingshot, shortly after 10am.
The University of Otago said internet and mobile service were limited at all its campuses, including in Dunedin, Wellington, Invercargill and Auckland, and they did not know when full services would be restored.
One New Zealand said engineers were working to restore internet and mobile service in Dunedin, and the issues affecting the two cables were unrelated and isolated.
"We're sorry for the inconvenience caused by this issue, our engineers are on site working to fix it and we hope to have service restored by this afternoon," a spokesperson said.
Some services were still working, the company said: "Eligible mobile customers will still be able to text using our satellite TXT service."
Contact Energy acting chief retail officer Michael Robertson said they were working closely with providers to resolve the issue as soon as possible.
In the meantime, the company said people should not unplug, power off or reset their modem.
Spark confirmed that only a small number of customers might be affected, if they were using Rural Connectivity Group towers, which were shared by all providers.
2degrees said all of its internet and mobile traffic had been moved to a different cable so its customers would experience minimal impacts.