Telecom's XT mobile network appears to be working again.
Around 80,000 customers south of Taupo have been without mobile phone services since around 4.30 Monday morning.
The telecommunications giant announced the outage on Twitter on Monday morning.
"Services are up and running and reports show our customers are using their mobile devices," said CEO Telecom Retail, Alan Gourdie.
"We continue to manage the network at a heightened level, reflecting the complex technical nature of today's fault, and in order to satisfy ourselves that it is delivering the level of service our customers expect."
Telecom has apologised for the outage, which happened after a technical fault affected a Christchurch-based technology component.
The company's been working all day to get the problem fixed, calling in specialists from overseas to help out.
Telecom says it's still doing final checks, but it believes the majority of services are functioning normally once again.
Gourdie says he knows it's critical to provide a consistent service and it apologises absolutely for the inconvenience the outage has caused.
Telecom say any XT customers still experiencing service issues
should try restarting their phone, by powering down then removing
the battery for several seconds, then restarting the phone.