Stink bugs' smell has been likened to coriander mixed with sweaty socks - and 15 made it to Christchurch alive.

They were supposed to have been gassed, but a cluster of stink bugs left Italy alive before slipping past New Zealand border control.

It was not until they got to Christchurch, hidden inside sealed panels on a mobile concrete plant, that the brown marmorated stink bugs (BMSB) were discovered.

A major biosecurity threat, the noxious pest releases a chemical when threatened. The smell has been likened to coriander crossed with sweaty socks.

GRAEME RANDLE The mobile concrete plant where the bugs were discovered was sealed and fumigated using methyl bromide.

In countries they have established, including Italy and the United States, the bugs have caused untold crop damage.

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Ministry for Primary Industries (MPI) data showed 26 bugs have been found since the September to April risk period started, but the Christchurch incident was the first detection beyond the border.

Gough Industrial Solutions, a Gough Group subsidiary, imported the Italian-made concrete plant, which had fumigation certification.

The plant arrived in Auckland, where MPI quarantine officers inspected it, on November 25. Goods from the United States and Italy require extra surveillance for stink bugs.

The cargo was green-lit and, the next day, the plant was trucked more than 1000 kilometres to Christchurch.

It was taken to the Gough Industrial Solutions premises in Hornby, where a staff member found the bugs.

There were 19 brown marmorated stink bugs, 15 of which were alive, including nine females – though they are non-reproductive during the northern hemisphere winter.

MPI was notified, a site investigation was carried out and the equipment was sealed in plastic and fumigated.

Investigator Carolyn Bleach said MPI was confident, based on the Auckland visual inspection, the stink bugs did not escape during the trip to Christchurch.

"The correct border procedures were followed at Auckland Port," she said.

MPI was following up with the fumigator and asking Italian authorities about their fumigation procedures.

Gough Group general counsel Graeme Randle said it was the first biosecurity issue Gough Industrial Solutions had experienced with Italian imports.

"It's pretty scary because it could easily have gone out to work had that one bug not been seen," he said.

"We're obviously really concerned as an importer that we don't introduce an unwanted pest into the country."

It was a reminder border controls and fumigation were "not necessarily absolute", he said.

MPI said it considered the Christchurch discovery a border intercept as the goods were taken to an approved transitional facility.