An Auckland civil engineer is asking questions about how a car was able to plunge off a four-storey carpark in Newmarket this week.

Two people are in hospital after their car fell off the top of the building, landing on the bonnet of a parked car below - and narrowly missing the two people in it.

Structural engineer John Scarry is calling for an urgent examination of the country's carparking buildings as a result.

He says modern parking buildings are supposed to have effective barriers against cars that lose control, but not all buildings comply with new engineering standards.

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John Scarry says of particular concern are barriers designed and constructed before 2002.

In many cases the only thing to stop a plunge off a building is wire mesh.