The New Zealand Transport Agency (NZTA) is promising to investigate whether more could have been done to prevent Thursday's bus crashes near Tekapo.
Two buses in a three-coach convoy rolled within a hundred metres of each other along State Highway 8's Tekapo-Twizel Highway shortly after 8.30am on Thursday. Fifteen people were rushed to hospital, including two who were seriously injured.
Other drivers on the road told RNZ conditions were treacherous and the highway should have been closed.
Transport Minister Simeon Brown has asked the NZTA to provide him with what it knew about the road's conditions and what motorists were told.
"Thankfully no-one lost their lives, but obviously there were some serious injuries, and I've asked for further information in relation to the information that NZTA had in terms of the condition of that road, and what information they were providing to motorists using that piece of road, particularly with the black ice."
NZTA transport services general manager Brett Gliddon said the agency would carry out a full investigation alongside police to see what the contributing factors were.
"If it sees that we need to make some changes to our operating procedures, we will. It's too early to say if the road needed to be closed prior to those accidents."
On Thursday, NZTA said the investigation would also include the condition of the two buses.