Waikato District Road Policing Manager, Inspector Leo Tooman, said both the Alfa Romeo and the truck were travelling south at the time of the collision.
"The truck and trailer unit had slowed as it approached a school bus in its lane that was slowing to turn right on to Otane Rd," Mr Tooman said.
He said both drivers would be interviewed by police later in the week.
Last night in Auckland, the managing director of New Zealand Fashion Week, Dame Pieter Stewart, asked the opening-night audience to observe a moment's silence in honour of Felicity Wren.
Felicity attended St Hilda's Collegiate in Dunedin before moving to Wellington for university. She is understood to have worked part-time at the Country Road clothing store.
A Fashion Week spokesman said she and Millie were to have dressed the models ahead of shows this week.
"They were to work with show producers backstage, helping models change in and out of outfits. The position might have come as a result of industry experience."
Friends of Felicity's sister Jess Wren, who is believed to be in London, shared their condolences on her Facebook page yesterday.
Georgia Maguire wrote: "I am so sorry to hear about your sister Felicity :( much love to you and your family."
Jayne Evans said: "So sorry to hear, Jess, your sister has such a beautiful soul and will be missed."
The Massey at Wellington Students Association said on Twitter: "Mawsa has crossed fingers for a full recovery for Millie. If you need any help during this tragic time please come see us."
Mr Thompson said the police were "facing a number of challenges" in notifying Felicity's next of kin living around the world.
He said officers were working with Interpol and other family members to complete the notifications.
"Members of the serious crash and commercial vehicle investigation units are working to establish what caused the crash."
