A New Zealand couple are waiting to hear if a mammoth potato they dug up has been recognised as the biggest in the world.

Colin and Donna Craig-Brown were weeding their garden at their small farm near Hamilton when his hoe struck something huge just beneath the soil’s surface.

As the couple knelt down and began digging around the object, Mr Craig-Brown wondered if it was some kind of strange fungal growth like a giant puffball.

But after prying it out with his garden fork, he scratched away a bit of the skin and tasted it.

“We couldn’t believe it,” Mrs Craig-Brown said. “It was just huge.”

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Colin Craig-Brown holds Doug (Donna Craig-Brown via AP)

When the couple lugged the mutant-looking potato into their garage and put it on an old set of scales, it weighed in at a remarkable 7.9kg. That is equal to a couple of sacks of regular potatoes or a small dog.

In the weeks since their unusual find on August 30, the couple’s ugly potato has become something of a celebrity around their small farm.

They have named the potato Doug and have even built a small cart to tow it around.

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Colin Craig-Brown built a cart for Doug (Donna Craig-Brown via AP)

“We put a hat on him. We put him on Facebook, taking him for a walk, giving him some sunshine,” Mr Craig-Brown said. “It’s all a bit of fun. It’s amazing what entertains people.”

A more official weigh-in at a local farming store put Doug at 7.8kg.

The current Guinness World Records entry for the heaviest potato is a 2011 monster from Britain that weighed in at just under 5kg. The couple say they have applied to have Doug recognised and are waiting to hear back.

Mr Craig-Brown said he does not have any secret gardening tips. Usually they throw a bunch of cow manure and straw on to their garden and see what happens.

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The potato could be turned into vodka (Donna Craig-Brown/AP)

He said they had been growing cucumbers in that area of their garden before the weeds took over and had not planted any potatoes. Doug must have been self-sown and quite possibly growing for a couple of years or more.

“It’s a mystery to me,” Mr Craig-Brown said. “It’s one of nature’s little pleasant surprises.”

But Doug has not proved easy to look after. As the couple showed the potato off, it began drying out and losing weight. Mould started growing from its wounds.

So Mr Craig-Brown cleaned up Doug as best he could and put the potato in the freezer, where it remains.

But the couple may not be done with Doug yet. Mr Craig-Brown, who is a home brewer, said he is keen to turn Doug into potato vodka.