Watch: Once in a lifetime Kiwi sighting on South Island's Heaphy Track

A tramper on the South Island's Heaphy Track was treated to the incredibly rare experience of seeing a kiwi in the wild - and in broad daylight.

Anya Bell posted to YouTube an encounter with what's understood to be a tokoeka kiwi, which could be seen walking around the track in front of her before darting back off into the wild.

Massey University kiwi expert Dr Isabel Castro said the tramper was lucky to have seen the bird - "oh my God, yes" - but was concerned at why the bird was out in daylight.

"Whether it's a young bird that is really hungry and is having to go out in the day because the night wasn't long enough to eat, or something else, it's not a natural occurrence," she said.

It was particularly rare to see kiwi in the wild in the South Island.

"In the best of circumstances, it's not easy to see a kiwi, and if you try to approach one, it's most likely response is going to be running away from you."

Kiwi Encounter manager Claire Travers agreed.

"My feeling is that the bird is compromised in some way and it's not feeling particularly well."

It could have been that the bird had been disturbed - but then there was the outside chance the kiwi was "just being curious", she said.