An investigation to understand how a snake got through New Zealand's border and onto an Auckland construction site yesterday is under way.

The snake has been formally identified as a juvenile male carpet python with no risk of reproduction.

Biosecurity New Zealand team manager aquatic and environmental health Michael Taylor said the snake was too large to be a hatchling but had not yet become sexually mature.

"There was nothing in its gut indicating it had not eaten for at least two to three weeks."

He said while an investigation is underway to determine how the snake got into the country, early indications suggest the snake had made its way into a pipe that had then been sealed at both ends before it was imported from Australia.

There is no evidence of any further snakes and there is no threat to the public.

Taylor said the 115cm snake may have been alive when it was found by the contractors.

"The snake was reported as dead when Biosecurity New Zealand was notified, but it appears it may have been alive when found by the construction worker."

Queensland University venom researcher Bryan Fry said it was most likely the snake came from Australia.

He said carpet pythons are found throughout Australia but with the greatest diversity found in the country's warmer areas.

A carpet python couldn't survive in New Zealand's cooler temperatures, he said.

"It wouldn't have hung on very long."

"Being late summer, it may have persisted for a little while. It may have gone up in somebody's attic but they need to be able to bask to be able to warm up enough to hunt properly and to feed.

"Even if it went up in somebody's attic, it would've slowly starved to death because it wouldn't get warm enough for it to be able to feed or bask."

He said snakes need to bask after eating in order to warm up and digest their food properly.

"Or else the food will just rot in their gut if they are too cold after a feed."

MPI said about one or two snakes get past the border each year, while a further four to eight are found at the border.

"They are normally not venomous and mostly arrive dead, due to treatment of imported cargo. Five snakes were detected at the border in 2020, all were dead."

The snake was found on a construction site in Papakura yesterday where contractors were flushing out a new pipe.

Contractors were flushing out the new pipe at the construction site in Papakura before laying it, which is when the snake came out.