A major fault at Sky Tower in Auckland disrupted phone and internet connections and forced several companies to use back-up systems on Tuesday.
What is thought to be a power surge and possible fire in a transformer room knocked out internet access to Vodafone's mobile and fixed-line internet customers throughout New Zealand.
Internet access for Vodafone customers came to a halt about 1pm for about 50 minutes.
The Sky Tower is one of Vodafone's major hubs for its entire network and is adjacent to Sky City.
The extent of the blackout is not clear, but Vodafone says other internet providers would have been affected.
Sky City says it may be Wednesday before it is known what caused the fault, which caused the evacuation of 200 staff, patrons and diners from its restaurant and gaming areas.
It says the power surge caused only smoke, but the Fire Service says it sent 12 engines and its crews issued a second alarm.
