An investigation into the substation fire which cut power to tens of thousands of Aucklanders will be jointly carried out by Transpower and Vector.

About 200 customers remain without power after extreme weather damaged power lines in the central and lower North Island yesterday.

When the lights go out over a large part of a city the size of Auckland, questions must be asked. How did this happen? Who allowed it to happen? Whose head must roll?

Vector and Transpower will audit vital equipment at power substations in a bid to identify other potentially vulnerable or problem areas within Auckland's beleaguered electricity network.

Energy Minister Simon Bridges says he is confident that lines company Vector acted appropriately in the wake of the power cuts in Auckland.

Vector has warned recently restored power users to expect to be 'dropped' from the system during peak times today, as a former chairman criticises the company.

Parnell hotels were full up with families and people suffering with health issues, said hotel staff in the area.

Auckland suburbs that have been without power for more than a day and a half face a further delay until the lights come back on.

Power should be restored to all Auckland suburbs by 5am tomorrow, lines company Vector said.

Here we go again. Another power emergency in Auckland, a city that's building a reputation for them, writes Grant Bradley.

The reason so many people lost power yesterday is because the substation at Penrose is very old and supplies a disproportionate amount of power to a large area of the city, says an energy expert.

Over the past couple of weeks, households have been receiving nasty surprises in the mail.

Hundreds of thousands of Transpower customers lost power today when backup measures failed to kick in while the company simulated a "catastrophic power failure".

Transpower has appointed chemical company executive Alison Andrew to replace chief executive Patrick Strange.

Electricity retailer Mercury Energy has announced its first across the board price cuts in a decade.

A widespread power outage is affecting homes and businesses in and around Hawkes Bay this morning.