A spokeswoman for lines company Top Energy, which is replacing power poles along SH10, said the cable was damaged by contractors working for Top Energy at a Chorus-supervised site.
Chorus spokesman Nathan Beaumont said up to 5000 customers could have been affected, depending on how much of the cable was cut through.
The company's immediate priority was get the service back up and running as soon as possible. Afterwards it would have a "friendly chat" with those responsible about cost recovery.
A Spark spokeswoman said customers in Te Kao, Kaingaroa, Kaitaia, Houhora, Whangaroa, Hokianga, Maungataniwha, Karikari, Mangonui and Taupo Bay were affected, while a spokesman for Vodafone listed the affected areas as Karikari Peninsula, Coopers Beach, Houhora, Te Kao and Taupo Bay. The lower half of the Far North, including the Bay of Islands and Kaikohe, escaped the outage.
Business owners in Kaitaia greeted the outage with frustration and weary resignation.
Ian Walker, who employs 26 staff across a number of businesses, said the outage had cut takings by as much as $8000. A bookshop, an electronics and appliance store and an IT business in particular were affected. Eftpos didn't work but staff were able to process some credit card payments by hot-spotting a laptop to a working cellphone.
He found it frustrating that, as with power, a single cable served the Far North. Kaitaia businesses lost about a week a year to various outages, a loss they could ill afford.
"But what can you do? Until someone stops talking about the infrastructure we need and starts doing it."
In an era of GPS mapping and cable-sensing equipment it was "bizarre" that someone could dig through a cable of such significance, Mr Walker said.
Meanwhile, patient care at Kaitaia Hospital was unaffected but communication with Whangarei was difficult, Northland District Health Board spokeswoman Paula Martin said.
Kaitaia Hospital's "particularly resilient" staff had business continuity plans in place and were well versed in dealing with outages.
Originally it was thought the cable had been cut by contractors carrying out drilling work at Taipa Bridge but they were not at fault.