The passenger, who suffered crush injuries to her legs, had to be freed by firefighters.
They cut open the front of the vehicle and removed tree branches to gain access to her.
The Mad Campers van struck the tree about 20m off the Kingston Rd shortly after 3.30pm.
The tree is beside an unsealed vehicle track in the Kingston Lake Camp, about 8km north of the township.
A St John spokesman said the women were transported to hospital by the Otago Regional Rescue Helicopter, one with moderate injuries and the other with minor injuries.
One of the women was trapped and appeared to be in ''a bit of pain'', but both were calm and coherent.
The driver told him she had felt pressured by a vehicle following closely behind, and had pulled off the road too quickly.
She had lost control on the slippery track, hitting the tree.
