Senior Constable Russell Halkett of Fairlie police said the family "deserve more understanding'' at this time.
Mid-South Canterbury area commander Inspector Dave Gaskin said the family was doing "everything they can'' to assist inquiries.
"It's a terrible tragedy for the family,'' he said.
"The loss of a child in any circumstances is distressing but you just can't imagine what they're going through right now.''
A serious crash unit has carried out a scene examination.
Police have refused to say what kind of vehicle was involved.
Inspector Gaskin asked that the family's privacy is respected and that further updates would be made through police.
"We'll get to the bottom of what has caused the accident in due course,'' he said, adding that officers were "nowhere near'' assessing whether charges would be laid.