A Western Australian egg producer made a rare find this week when she cracked open a giant egg and found another full egg inside it.

Blythe Calnan, from Runnymede Farm in Binningup, 150 kilometres south of Perth, was collecting eggs on Sunday morning when she found the prodigious egg.

"This egg was absolutely 'eggnormous'," she said.

"The biggest egg we've had on the farm was 119 grams — we call that 'Eggzilla' — and this egg would have been even bigger than that."

Egg abnormalities can happen all the time, but a double egg is rare. ( Unsplash: Kelly Neil )

Ms Calnan shook the egg slightly and knew straight away she had found something special.

"When I gave it a bit of a rattle I could actually feel something quite solid inside, so that's when I first realised something was quite different," she said.

It is not clear which of her chooks produced the massive egg, but all the hens were found alive and well upon inspection.

"I did do a full check of the hens to find the victim of this egg," Ms Calnan said.

"But no one presented with a complaint, and all cloacas were intact and in good working order."

Hen could have been having an 'off day'

Ms Calnan believes something went wrong during the contraction process when the hen attempted to push the egg out.

"So instead of that contraction starting from the top and pushing the egg, out it started from the bottom and pushed the egg up to where the eggs are formed," Ms Calnan said.

"Then she's gone to build the next day's egg it's built around the existing egg."

Meg Miller is the editor of the Australasian Poultry magazine and said she's never seen a double egg.

"It's known as an egg normality, it's quite recognised but it's not a common," Ms Miller said.

"You're more likely to have a shell-less egg."

She said the hen may never produce a double egg again.

"It just could have been an off day," she said.

This huge egg weighing 176 grams was found on a farm in Queensland and turned out to be an egg inside an egg. ( Supplied: Stockman's Eggs )

Unusual, but not unheard of

There have been several other cases of egg producers sharing their delight of finding a double egg across Australia.

Elena Di Bonaventura was shocked to find out the giant egg was actually two-in-one. ( Supplied: Brad Baldock )

A farmer on the Atherton Tablelands in North Queensland found a double egg that weighed 176 grams — the largest that farm had ever produced.

Egg farmers in Albany, on WA's south coast, were shocked when they discovered a double egg in March this year.

Elena Di Bonaventura, who began working for Albany Fresh Eggs in July 2017, said it was the only time she had ever seen a double egg.

"I was like 'oh my god, what is this?'" she said.

"I was very surprised.

"It was massive. I think 160 grams something like that, bigger than a jumbo egg."

Ms Di Bonaventura said some workers who had been at the farm for almost a decade were equally surprised.