A Spark NZ outage is affecting an unknown number of customers in the central North Island.
Land lines and 0800 numbers are being affected in some areas.
"We are aware of a problem affecting some customers not being able to make or receive calls. Our technicians are currently investigating," Spark says on its website.
"We apologise for any inconvenience."
Spark says large businesses that operate on the Broadsoft platform are mainly affected.
People with copper landlines should not be disrupted and the mobile network is operating normally.