The Ministry for Primary Industries is investigating reports that a grandmother knowingly deceived biosecurity staff in order to sneak an illicit item into the country.

It wasn't weapons or an endangered species the woman is supposed to have brought in: it was an egg yolk-filled mooncake.

MPI was alerted to the incident after a post online caused a flurry of comments from outraged readers.

In the post, shared on Reddit, the author says her grandmother had thought up an elaborate ploy to get her mooncakes into the country.

"The biosecurity officer asks if her mooncakes have yolks, and she says no. When they cut into one to check, she provides one, they cut into it, no egg yolk and she's free to go - little knowing that she gave them the one she bought especially without yolk exactly for that purpose," the person wrote.

"All the others have yolks."

MPI's website clearly states that egg-related foods - including raw yolk - are "not allowed into New Zealand". The website states that mooncakes with whole egg are allowed if they "been commercially manufactured and packaged, packaged by the manufacturer, in its original packaging unopened, does not contain meat, and does not require refrigeration". However, the items must be declared and inspected.

The post on Reddit elicited many angry comments from users.

"Sad how some people just have to go to extreme lengths to break the rules... even though it's clearly possible to have mooncakes without the yolks anyway!" wrote one person."

"Things like this just end up making it harder for biosecurity to operate, ruining the experience for everyone else. Thumbs down for this person and their grandma," wrote another.

In the comments section, the Reddit user responsible for the initial post, which appears to be a screengrab from Facebook, wrote that MPI had received numerous complaints following the post and were "looking into it".

An MPI spokesperson confirmed they had been alerted about the event and were following up on the information.

"In general, we take a hard line on travellers who fail to declare items that could bring invasive pests and diseases into New Zealand," the spokesperson said.

Travellers who intentionally bring biosecurity risk goods into the country can be denied entry into the country or face a fine of up to $100,000 and/or five years in prison.

It is unclear whether the person who posted the story to Reddit was the person who wrote the original post.

Newshub.