"We see scrap metal consignments as high risk for hitchhiking pests, insects and soil, which is why MPI requires all imported scrap metal containers to be fumigated at their first port of arrival," Gwyn said.
Last year, four snakes were found in cargo in New Zealand, a MPI spokesman said.
All were dead on arrival.
Since 2000, there had been about 60 snake interceptions in the country, he said,
"When you say 60 it's probably a bit of an exaggeration because you find the skins, and bits of snake and stuff like that, so it may have been in the goods for some time."
Although most snakes were found dead on arrival, the odd alive snake would make its way into New Zealand.
If that was the case, they would be killed.
"If you open up a container ... and a snake was seen, they'd just close it up again and fumigate it," he said.
Most snakes came into New Zealand from South East Asia and China, followed by Japan and Australia.