Police said the women were travelling east on State Highway 25 on Tuesday when a car coming in the opposite direction drifted over the centre line and the vehicles collided.
The sole occupant of the other car suffered serious injuries and was taken to Waikato Hospital.
Mr Strydom said Jani and Natasha had been best friends since starting school together in South Africa, aged 4.
Both families emigrated from South Africa in 2004 when the girls were 9. The Strydoms came to Auckland and the von Wiellighs moved to Adelaide.
"They kept in touch all the way through and visited back and forward," Mr Strydom said.
"They were both the most amazing and loving girls. They were such an example of a good, perfect friendship."
Mr Strydom said they called each other BFFs, or best friends forever, and had planned to go on an OE together when they graduated university. "It's just tragic that they both had to go."
The girls had been having the "time of their lives" on the road-trip, Mr Strydom said.
Natasha was entering her third year at Massey University in Palmerston North, where she was studying towards a Bachelor of Science in agricultural science and zoology.
"She was passionate about animals and the outdoors," Mr Strydom said.
The girls' road-trip was due to end in Palmerston North, where Natasha would have shown Jani where she was studying and her new flat.
"They both touched the lives of everyone they got in contact with," Mr Strydom said. "It's very, very hard for us."
He said his daughter was "an absolutely bubbly person with a contagious personality that was indescribable".
Yesterday, Jani's parents arrived in New Zealand and were staying with the Strydom family in their Auckland home.
Jani's father Erich von Wielligh said his "bubbly" and "happy" daughter had been so excited to visit Natasha.
"They were friends from kindergarten and we moved to Australia, and the Strydom family moved to New Zealand, but we kept contact and the girls were always visiting each other on holidays."
Jani had been due to fly home next Monday.
"They had a good time, we Skyped the other evening, and they were excited about the day and what they were going to do."
Mr von Wielligh said his daughter was a "keen student" who was in her third year at Flinders University in South Australia, where she was studying law, international studies and languages.
She was planning to study for six months in France at the end of the year, he said.
Inspector Dana McDonald said alcohol and speed had been ruled out as factors contributing to the crash.
A Massey University spokesman said Natasha was a popular student who was active in the surf, snow and skate club.
She had stayed at McHardy Hall in her first year and had applied and been accepted to be a residential adviser in the halls this year.
"She had a bubbly, friendly personality ... her death will come as a shock to her fellow students and the university's thoughts are with her family and friends."
- Additional reporting Nikki Papatsoumas, NZME.
