Ms Chhetri and her son died at the scene, while the driver and a 10-year-old girl, were airlifted to hospital.
The three passengers in the second vehicle, travelling south, were transported to hospital - two by helicopter and one by ambulance.
The President of New Zealand's Non Resident Nepali Association, Baburaja Maharjan, said he was extremely saddened to hear about the accident, which claimed two members of Christchurch's Nepalese community.
"We extend deepest condolences to family members and we express immediate recovery of other Nepalese friends seriously hurt in the accident."
Mr Maharjan said the family was returning home to Christchurch after visiting friends in Queenstown and Dunedin when the accident occurred.
Originally from Bhutan, they had come to New Zealand as refugees, he said.
A serious crash investigation is continuing into the crash.