The child fell about 20m down a hill and off a cliff about 6.40pm on Saturday while walking the Mt Somers Track which links the popular Pinnacles and Woolshed Creek huts.
A rescue helicopter was dispatched and airlifted the child out of the area.
Hato Hone St John said the patient was transported to Christchurch Hospital in a moderate condition.
It is understood the child was part of a group of families tramping in the area.
Mt Somers Walkway Society chair Robert Schikker said the incident was a reminder of the risks associated with alpine environments.
Content about the walkway on social media implied it was an easy area for tramping.
"It’s great for people to use it, but people have to be well aware it’s an alpine environment," Schikker said.
Large numbers of young families have recently been tramping in the area.
On the Mt Somers Track from Staveley to Mt Somers, there are two huts for trampers to stay - the Pinnacles Hut and the Woolshed Creek Hut.
Schikker recommended anyone doing the trek to the Pinnacles Hut should carry a personal locator beacon as cellphone reception is variable in the area.
