When Arlene Barbeau cracked open one of her home-grown eggs this week, she never expected to find a second egg inside.

The owner of Parklands Produce in Te Puna says she was rustling up a meal on Monday and cracked opened a largish egg from one of her chooks.

The egg inside an egg, discovered by Arlene Barbeau.

'I thought it might have been a double yoke because it was so big, but inside was another complete egg.

'It's never happened with our chooks before so I searched on the internet and learnt it was a rather rare occurrence.”

The inside egg measured about 4cm long, while the outer egg was roughly 6cm long and had a yoke and white in it which 'was still very delicious”.

With 23 chickens Arlene has no way of knowing which chook laid the extraordinary egg but says all of them appeared to be fine and healthy.

However, she certainly has some sympathy for the chicken.

'The size of the egg was huge, so I thought it must've hurt. I think it'd be like a woman giving birth to a 12 pound baby,” says Arlene.

The cause of this rare phenomena is called counter-peristalsis contraction and happens when a new yolk is released early while an existing egg is still forming and not yet been laid.

This causes a contraction and the two eggs meet in the reproductive tract. Both are then given a layer of albumin (egg white), membranes and a shell before being laid.

Parklands produce owner Arlene Barbeau and her grandchildren Chelsey and Joshua with the egg inside an egg.