Far North dairy farmers lost hundreds of thousands of dollars in revenue during yesterday's blackout, but the situation would have been dire if it had lasted more than 24 hours.

Farmers of New Zealand president Ian Walker described the power cut as a "massive economic hit" that impacted on a community already paying some of the highest electricity charges in the country.

"This sort of thing is Third World. The areas of this country that actually create wealth like the Far North are the most ignored," said the Kaitaia dairy farmer.

"This is a community that needs every dollar it can get but our infrastructure is not good enough. It's unlikely what's going to be lost, not just by farmers, but businesses and others will ever be recovered."

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Mr Walker said a typical dairy farm in the Far North with 300 cows producing 6000 to 7000 litres of milk could lose between $3500 and $4000 a day if the animals were not milked.

Other potential costs for farmers were having to put their cows on a feed, possible electrical damage to chillers when the power came back on, and health risks to cows. Few dairy farmers have back-up electricity supply because of the cost.

Fonterra was yesterday assessing the number of farms affected by the power cut but a spokesman said the company would collect milk from farms that were able to supply it.

More than 1000 farms in the Far North supply milk to Fonterra.

Milk from yesterday could be collected today if it was under the acceptable temperature. Some Far North farmers were able to milk using electricity from alternative sources such as tractors.

The spokesman said if a farmer was forced to dispose of milk as a direct result of a power cut, their own insurance company would cover the cost.

Top Energy said it could not supply emergency power from its geothermal power plants at Ngawha Springs because it was connected to the national grid.

"The system is set up for Ngawha to run with the Transmission network connected. Unfortunately, until we increase the size of the power station, it can only operate with that connection to the national grid," spokeswoman Philippa White said.

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A $300 million Ngawha power station expansion should boost its output from 25MW to 75MW - more than the Far North's peak demand of 70MW.