Peak power demand has surged to new highs as the North Island feels the icy grip of winter and the South Island continues its slow recovery.

In the South Island about 1000 homes are still without power.

In snow-hit South Canterbury, 104 people without power in their homes spent the night in Timaru motels paid for by the district council. The average stay in a motel was two nights.

The weather of the past two weeks, plus power cuts in both the North and South Islands and record power demands, have raised fresh questions about the security of the country's supply.

On Monday, record power consumption put huge pressure on electricity generation.

Peak power demand in Auckland and Northland yesterday morning jumped 7 per cent from last year, Transpower said.

Wellington's peak power demand rose 6 per cent and the upper South Island 4 per cent. Electricity demand is forecast by Transpower to grow by 2 to 2.5 per cent annually.

Transpower spokesman Chris Roberts said the security of supply was not adequate and that was why $3 billion to $4 billion was being spent to upgrade the national grid over the next four to six years.

Energy analyst Bryan Leyland said the country was short of generating capacity because of a growing reliance on electricity and a lack of new capacity being created.

"So a relatively small thing going wrong can put us on the edge of disaster. The general feeling is that the power system has got a lot less reliable in the past 10 years."

The country should be able to handle the pressure of a one-in-five or one-in-10 year weather event, Mr Leyland said.

A new generation station being built at Huntly would only "get us back to the situation we should be in right now".

Auckland needed a back-up energy system and its cost would be about the same as that of the recent power failures, Mr Leyland said.

He dismissed calls for powerlines to be put underground in snow-prone areas, saying the snowstorm which knocked out power in rural Canterbury was an exceptional event.