A ride on the turret of a privately-owned tank turned to disaster for a prominent Auckland family, when the mother landed in hospital.

Vicky Bethell and her 3-year-old daughter, Jessie, were crushed by the tank's gun turret at her farm in Bethell's Beach on Auckland's west coast.

A week later, Bethell is still in hospital with four fractured ribs, two fractured vertebrae and other injuries. Bethell, an artist, is expected to be discharged this week.

Bethell - from the family after whom Bethell's Beach is named - was among a group of people who were riding on the tank, owned by Charles "Tankboy" Knight.

The incident happened the day after a memorial service for Bethell's husband Ross, who died in October last year. The tank was driven by Knight, who declined to comment yesterday.

Live-in nanny Kirdy Molan, who had been working for the family for less than a week, was behind the tank when the accident happened.

She said about 10 people were riding on it in a paddock near Bethell's house when the turret came loose.

It swung around, flinging off the six people on the cannon and slamming the hatch down on Bethell and her daughter.

Both were trapped but Bethell's stepson and friends quickly lifted the hatch. "It's a good thing the guys were there," said Molan.

Bethell's nephew, Mitch Rickard, is a volunteer firefighter and training to be a paramedic. Molan said it was fortunate he was there to help.

Safety staff from a nearby television crew arrived to help, and ambulance, firefighters and police followed soon after.

The Westpac Rescue helicopter was called to airlift Bethell to Auckland Hospital.

Rickard said Jessie escaped with only bruising on her leg. She is being looked after by Molan, Rickard, and Bethell's stepson John.

Knight stores the tank and an armoured truck at Te Henga farm, the Bethell's Beach property used as the base for his military equipment and entertainment company, Tankboy TV.

The business stages action entertainment shows.

Buying a tank? What you should know

Buying a tank can be complicated and expensive.

Jonathan Lahy-Neary, who operates five armoured vehicles at a tank driving range in Christchurch, said would-be owners need permits and a firearms licence. To make them legal for public highways, they need a warrant of fitness or New Zealand Transport Agency certificate of fitness.

Most tanks are bought overseas and importing them is a large part of the cost. A big tank such as a British Centurion or Russian T-55AM2 will cost between $100,000 and $200,000. But the fuel costs are "horrendous," said Lahy-Neary, with the fill-up price reaching $2000.

Tanks and military vehicles occasionally sell on Trade Me an Alvis Spartan armoured personnel carrier and Alvis Stalwart MK2 are currently listed.

The New Zealand Defence Force has 105 Light Armoured Vehicles 88 wheeled armoured vehicles with 25mm cannons. Lahy-Neary said they were not classified as tanks because they did not have tracks or big enough guns.