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People returning to the 1km area, which has been restricted since the tornadoes struck soon after noon yesterday, are being warned to take "extreme care when checking their properties''.
About 250 people were left homeless and thousands of homes were without power after the violent storms, which are estimated to have caused $11 million worth of damage.
Prime Minister John Key, touring the area today, said the loss of life could have been far greater.
"It's far more significant than a very bad storm where you have a few trees down. It's something you might expect to see in the midwest of America, but not in Hobsonville,'' Mr Key said.
"I think we'll take a step back and retrace our steps and ask the obvious questions: What was in place in terms of weather forecasting? Did we miss anything? What does that mean in terms of people on the workplace and the likes?
"I suspect in the end it will come down to - as it does in America which is much more prone to these - that they're a sort of random act of nature.''
The clean-up continues this evening as roads are re-opened and electricity restored to large areas without power more than 24 hours.
Vector's high voltage network is expected to be switched back on tonight, though 470 customers were still without power at 6pm.
The company said some of those homes would have electricity tonight and repairs to its low voltage network were "ahead of schedule''.
"Vector will have a more definitive idea of restoration times by tomorrow,'' it said in a statement.
"When the [low voltage] network is relivened, Vector is then in a position to begin looking at customers' service lines to ensure they are safe and compliant. Once the service lines are safe, properties can begin to be restored.''
The three men killed on a construction site when the tornado ripped through Whenuapai and Hobsonville were named as Tom Stowers, 42, Keith Langford, 60, and Brendon Johnson, 22.
The men, from Hawkins Construction and subcontractors Vuksich and Borich Civil Engineering, were crushed by a large concrete slab as they took shelter from the tornado.
Four other men working on the building site were hospitalised; one remains in a stable condition and three have been released, the company said tonight.
"This has been a terrible tragedy for the families of those killed and injured and everyone involved in the project is deeply shocked and saddened by what has happened,'' Hawkins Construction general manager Dan Ashby said.
The company has offered support to others in the area affected by the tornado.
Auckland Council programme adviser Jan Ziegler-Peri said 66 people had registered with the Massey Leisure Centre recovery centre.
Work and Income has arranged for people who have been displaced to stay in motels for up to two nights.
Some West Aucklanders affected by the tornado said they felt they were not prepared for the emergency.
Wamairie Rd resident Rhys Hogg said: "We're lucky we've got gas cookers. And the water's still on, but if the water was off we'd be in trouble.''
The family had been caught without an emergency kit, but that was certainly something they were "going to get''.
"It makes you think about, if it was worse, what could've happened.''
Just up the street, Kate Dunn had similar concerns.
"[We were] not as prepared as I would have thought. We've got lots of food but it wasn't until later that we got out a gas cooker and one of the attachments was missing that made us aware that we probably need to be a bit more prepared than we were.''
- By Kieran Campbell, Lucy Bennett and Matthew Theunissen of APNZ
By the numbers
- 250 people left homeless
- Thousands of homes without power; 470 still in the dark tonight (Fri)
- $11 million worth of damage
- 1km zone cordoned off for more than 24 hours
- 510 homes at Whenuapai and Hobsonville assessed for damage
- 22 homes found to have ``major damage``
- Five dogs and two cats being cared for at the council's West Auckland Animal Shelter
Where to get help
- Massey Leisure Centre recovery centre to reopen at 10am tomorrow
- Victory Church Recovery Centre will not reopen
- Residents requiring welfare assistance can report to the Wiseley Rd and Clark St incident control point
- The Government helpline can be reached on 0800 779 997