Emergency services were called around noon after the girl fell into Marian Creek in the South Island's picturesque Fiordland region.
Southland Area Commander Inspector Mike Bowman said the girl was quickly found and lifted out of the water. A doctor was flown to the scene, but efforts to resuscitate her failed, he said.
"This has been a traumatic event for those involved," Bowman added, praising members of the public who helped find her in the water.
The creek, around 35 kilometers (22 miles) from Milford Sound, is in a rugged part of the Fiordland National Park in New Zealand's Alpine region.