Contractors have unearthed an unexpected treasure on a building site in South Canterbury.

Bones from both a male and female Moa were found buried in the clay.

There are dozens of bones from both a large female and a smaller male in what's now a secret location, which is believed to have once been an ancient swamp.

Curator of Natural History at Whanganui Regional Museum Mike Dickison said it's a brilliant find.

"It's still about the only place you are still finding Moa bones, I guess how complete the skeleton's are will determine how important scientifically the find is and also the condition they're in."

A pelvis and ribs were amongst the dozens of bones found on the site.

But Mr Dickison said it's not quite such a surprising find:

"These bones are turning up more often than most people would think, nevertheless there's a finite supply, we're not making anymore so one day we will probably have discovered the very last Moa bones there are to discover."