More than 2,000 phone lines in the Auckland suburb of Pt Chevalier have been severed, after a contractor cut through copper wires at a nearby exchange on Friday.
The fault, which Telecom describes as a dramatic interruption, will leave hundreds of home-owners and businesses without landlines and dial-up internet for days.
A Telecom spokesperson, Mark Watts, says each of the copper wires will have to be fixed individually and emergency measures are being put in place.
Mr Watts says customers with medical conditions can be supplied with loan mobile phones, and provisions are being put in place with St John and its Lifelink service.
He says the company is hoping for services to return by the middle of next week.
St John Ambulance says people who rely on its emergency Lifelink service should consider staying with relatives, after a massive phone outage.
The ambulance service's Maggie Calvert says Telecom has offered to give cellphones to those who use the emergency-call device.
But she suggests such people should be watched over by family members.