A company replacing power poles is believed to have severed a fibre cable, cutting landlines, internet and cellphone networks to much of the Far North.
The Chorus-owned cable was cut about 10.15am.
Spark customers in Te Kao, Kaingaroa, Kaitaia, Houhora, Whangaroa, Hokianga, Maungataniwha, Karikari, Mangonui and Taupo Bay are affected.
A spokeswoman said the fibre line also supplied other providers so people using other networks could be affected.
Chorus had dispatched a technician and hoped to have the cut fixed by 6pm.
People using the Vodafone and 2degrees cellphone networks are also affected but some calls are getting through.
Originally it was thought the cable had been cut by contractors carrying out drilling work at Taipa Bridge but it was later found they were not at fault.
The southern part of the Far North, including Kaikohe and the Bay of Islands, is not affected.