Muddy Buns, Dirty Dirty Bread, or Zang Zang Bao as they're known in China, are creating a social media frenzy and driving a further craving for butter around the world.

Fonterra Edgecumbe is all geared up to handle this global trend and is commissioning a new butter line which will nearly double the factory's butter sheet production from 4500 metric tonnes to 7000 metric tonnes.

Fonterra general manager marketing, global foodservice, Susan Cassidy said the product could best be described as a chocolate croissant.

"People love the flaky chocolate pastry that's coated in rich chocolate ganache and sprinkled with cocoa powder.

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"It makes it impossible to keep your face clean while eating. They are popular with celebrities who have taken to social media to share images of their 'muddy bun face' experience."

Cassidy said demand for butter was as strong as ever.

"Even in temperatures of minus ten degrees, crowds of people are queuing for hours to get their hands on their Muddy Bun."

Edgecumbe's operations manager Allan Muggeridge said the first butter sheet would roll off the new butter line on September 1.

"We've been watching demand for butter build for a number of years now. The building part of the project started in May so it's been a quick turnaround to get it up and running."

Fifteen local contractors have been employed to complete the expansion at the site, which employees 380 people.

"It's been a real boost to the local business community, especially after the rough past 12 months Edgecumbe has had," Muggeridge said.