Key Points:

A power blackout today across Auckland's eastern suburbs could not have come at a worse time for trade, a local business group says.

About 74,000 homes and businesses were hit by the major power outage, stretching from Mt Wellington to Newmarket.

The outage is believed to have started from a transformer fault at 1.10pm, a Transpower spokesman said.

Newmarket Business Association head Cameron Brewer said it was a blow for many businesses, particularly given the recession.

"When you consider everything from wasted restaurant meals, employees unable to work, wiped computer documents, and missed electronic sales, the cost would have to be several million," Mr Brewer said.

"Having a secure electricity supply is absolutely critical for business. Given the cost of power, business now deserves a full explanation."

Mr Brewer said assurances were given after a major blackout in June 2006 that maintenance would be improved and risk would be spread.

During today's incident, staff at National Bank in Newmarket gathered together and kept calm, personnel manager Jon Randles said.

"We had no idea when the power was going to come back on. Due to the OCR (Official Cash Rate) announcement, we'd been doing a lot of work for customers and we were trying to catch up on the backlog, so this has thrown us even further behind.

"After the previous big power outage in Auckland in 2006, I thought there would be some kind of contingency plan," Mr Randles said.

Many day care centres were forced to close for the day, and staff at Bear Park infant toddler centre in St Heliers had to call parents to collect their children.

Viv Withell, who has a 17-month-old son at Bear Park, said while it was business as usual in her office in Ponsonby, she had to drop everything to collect him.

"I'm very busy today and I'm expecting bookings. I've got no other option but to bring my son back to the office if the power is out at home," she said.

Meanwhile at Greenlane Hospital some appointments have had to be cancelled.

A spokesman from Auckland District Health Board (ADHB) said the Greenlane Clinical Centre was affected.

"The generators are running, essential services are in place and all patients are safe.

"Some outpatient clinics which do not require access to a computer system are running, but most others have been cancelled.

"Auckland City Hospital was also affected with some computer systems offline, however all critical services are running and patient safety was not affected," the DHB spokesman added."

The cut happened after a substation in Penrose went down.

Transpower spokeswoman Adele Fitzpatrick said one of the three transformers was out of action due to routine maintenance. The other two were handling the load until a malfunction in one of them that caused the third to trip.

Fire communications shift commander Mau Barbara said firefighters rescued four sets of people stuck in lifts as a result of the power cut.

He said two were in the Central Park complex in Penrose, another was in the Wella building in Ellerslie, while the fourth was on Newmarket's Broadway.

Mr Barbara also said fire fighters have responded to 15 alarm activations, some of which were burglar alarms mistaken for fire alarms.

He said fire fighters were also called to power lines on fire in Parnell and a smoking transformer in Ellerslie.

The power cut knocked out traffic lights across east Auckland from Onehunga to Orakei including Balmoral and Greenlane.

Traffic lights were also reported to be out in St Helliers, Kohimarama and Mission Bay.

Police said too many sets of traffic lights were out to arrange officers on points duty.

At 1pm shops in Remuera closed doors and were in darkness.

Reports that Sylvia Park shopping mall in Mt Wellington had been evacuated were untrue.

"The power was down for an hour and a-half. A lot of customers hung around in the mall as it's light and airy and we had emergency lights running on batteries," centre manager Jonathan Douglas said.

Staff at the deLongi premises in Mt Wellington were being sent home because of the outage.