The New Zealand Ornithological Society's records appraisal committee has accepted as probable a sighting near the town of Reefton, China's official Xinhua News Agency reported.
New Zealand's Threat Classification System this month changed the South Island kokako's classification from "extinct" to "data deficient" based on the Reefton sighting and 10 other claimed sightings.
The last confirmed sighting of a South Island kokako was in 1967.
"We can't say that the South Island kokako is still alive. But this is the best sign yet that it is," advocacy manager Kevin Hackwell of the Forest & Bird conservation group said.
New Zealand is thought to have lost more than 50 bird species since the 14th century Maori settlement and later European settlement, and if one of those extinctions turned out to be incorrect, "it would be incredibly good news," Hackwell said.
The South Island kokako -- a dark bluish-grey bird with a long tail, short wings and orange wattles on its face -- is not a particularly good flier and prefers to use its powerful legs to leap and run through the forest, the New Zealand Department of Conservation said.