A change to Cadbury's Marshmallow Eggs has been criticised for it's new shape, with people lashing out online about the brand calling it a "nightmare".

Cadbury's Marshmallow Eggs have taken on a new shape. Source: Cadbury

People have taken to social media to complain about the "disgusting" changes to Cadbury's Marshmallow Eggs, asking - since when do eggs have a flat side?

One person said Cadbury needed to get its act together and "stop butchering your products", and others complained about how they liked to pull the two halves apart to eat it.

"Shame on you, since when are eggs flat on one side," a commenter said on Facebook.

Following the closure of Cadbury's Dunedin factory, the brand's Marshmallow Eggs are now made in Australia with new equipment which meant the shape had to change.

However, while the new eggs appear to look like half an egg, the multi-egg trays are the same weight at 150g and contain the same amount of marshmallow and chocolate as the old ones, Cadbury senior marketing manager Mel Yates said.

The 175gm and 325gm sharepacks have changed in weight, but their recommended retail price has also changed so that they’re now cheaper per gram than the old eggs.

"The sharepacks now offer more chocolate and marshmallow bang for your buck than before," Ms Yates said. "They will still have the same marshmallow fluffiness and yolk that Kiwis love, and they’ll continue to be covered in delicious Cadbury chocolate."

"While we would like to have continued making them the same shape, the age of the previous equipment has meant we’ve invested in more modern equipment which will ultimately deliver more consistent quality."

The new shape was developed by Cadbury's Dunedin team, and several members of that team had moved to Melbourne with their families to continue overseeing production of the Cadbury products, Ms Yates said.

"It’s a change that would have happened anyway, the factory closure just brought the timing forward," she said.

She did not comment on exactly how many people had complained, but said, "as with any change, some people will be disappointed by the new shape."