Broadband was restored to Waiheke at 2.35am, Chorus says.

Last night, as the network provider struggled to pinpoint the exact location of the fault on the Howick-Waiheke cable, there were fears it was undersea.

But in the final event, the fault was resolved by replacing a segment of cable on land.

"The fault was seemingly near Maraetai on-shore near where the cable lands. We replaced a 300m length of fibre," a Chorus spokesman said this morning

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The cable issue, which hit around 3pm yesterday, also caused Spark to lose nearly all of its mobile service on the island.

"Five out of six Spark mobile towers on the Waiheke are experiencing a loss of service due to the Chorus network issue," a Spark spokesman said about 8pm.

"We believe this is affecting a large majority of Spark Waiheke Island customers and apologise to those impacted."

Spark uses the Waiheke-Howick cable for "backhaul" or to connect cell towers on the island to its main network, meaning it's likely Vodafone and 2degrees service was also compromised too (neither could immediately confirm).

Resident John Martin - a security practice lead with IBM NZ - said he was "Definitely affected yesterday. I was about to go into Webex[an online video call] with Australia with 20 people waiting for me. I reverted to personal hotspot, but does put a dent in ones confidence for working at home on Waiheke Island."

The sustained outage raised some disturbing questions, Martin said.

"This morning I was talking to my colleagues, who support the Civil Defense for the Island, as volunteers," the IBM man said.

"This would have affected Civil Defense had there been a disaster situation because they use the Internet to communicate information, to remote sites.

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"Plus, St John's Ambulance as they use the mobile services to communicate with GPs and calls out.

"And lots of point-of-sale would have been down. For example, Countdown and petrol stations.

"Lots of questions have to be asked about the resilience of Waiheke Island Internet connection."

Undersea fibre optic cable cuts in Sydney Harbour in 2001 and off Tonga this year were both blamed on ships' anchors being dragged.

The Tongan cable was cut on January 20. A repair ship arrived on February 3, then took about 18 hours to splice a repair.

Late yesterday afternoon Chorus confirmed 4000 Waiheke households were without broadband after a suspected cut in fibre from mainland Auckland.

Several Chorus telecommunications services were affected, including both copper and fibre broadband on the island.

Waiheke's Ultrafast Broadband build was completed in 2016, with more than 5600 local homes and businesses connected.