Three people have reportedly been killed and seven injured after a tornado hit west Auckland this afternoon.
A Fire Service spokesman said two of the people died when a concrete slab landed on a truck at Hobsonville, in the city's northwest.
The deaths occurred at a building site where a new high school is being constructed.
A shaken construction worker Sam Nuthall, who was working at the high school site, said he believed two people had been killed at the site.
He and his workmates saw big dark clouds and thought it would just be a rainstorm but were then forced to shelter between a block wall and a truck.
"You couldn't see it coming ... there was debris flying everywhere, steel getting thrown around," he told Radio New Zealand.
"I've never been in weather like that before."
He said there were 50 to 80 people on the site and there were a few "pretty bad" injuries.
The dead workers were not from his company, he said.
The Hobsonville Point secondary school, due to open in 2014, is a public private partnership between the Ministry of Education and the Learning Infrastructure Partners consortium.
Hawkins Construction were part of the consortium, along with ASC Architects.
The Fire Service spokesman said there were reports of people trapped in buildings after damage and roofs lifting when the tornado hit.
It was working through scores of calls after the tornado hit about 12.15pm (1015 AEDT).
3News reports roofs of around a dozen houses were either completely or partially gone and debris is spread across streets near Wallington Way.
An ambulance communications spokeswoman said it was dealing with seven injured people.
A heavy thunderstorm swept over parts of west Auckland with downpours causing localised flooding in some areas.
Weatherwatch.co.nz says another band of thunderstorms and torrential downpours are moving back to the area.
"We are advising people to remain indoors until the torrential rain and possible thunder has passed, most likely over the next hour or two," head weather analyst Philip Duncan said.