A 2-year-old in the back seat of the Nissan Primera was thrown from the vehicle during the Wednesday crash.

The 2-year-old girl who died in a Hawke's Bay crash did not appear to have been wearing a restraint.

The girl, from Flaxmere, died on Wednesday afternoon after being thrown from a rolling car in a "violent crash" on the Hawke's Bay expressway.

Senior Constable Corey Ubels said there was a restraint in the rear of the car and police were looking at the possibility that the girl was not restrained at the time of the crash.

MEGAN HUNT/ FAIRFAX NZ The passenger's side of the Nissan Primera is crushed after rolling during the crash on Wednesday.

"It appears she may have been unrestrained," he said.

Police were appealing for witnesses to the leadup to the crash, and the crash itself, he said.

The crash occurred on the expressway between Omahu Rd and Flaxmere Ave just before 5pm.

MEGAN HUNT/ FAIRFAX NZ A child's car seat in the back of the damaged vehicle.

Police say the Nissan Primera car appeared to have crossed the centre line, rolled and ended up in a ditch. The cause of the crash is still under investigation.

The girl's mother and aunt were taken to Hawke's Bay Hospital with moderate injuries. They remain in hospital today in a stable condition.

The young girl died at the scene, after attempts to resuscitate her by ambulance staff and motorists who had stopped to help.

MEGAN HUNT/ FAIRFAX NZ Scene of the crash, on the Hawke's Bay expressway.

Police will not name her until all family have been notified.

Ubels said police were also calling for any witnesses who may have seen the crash.

"This was a busy time of day on the expressway and we are keen to speak to anyone who may have seen what happened. We're unsure at this stage if any other vehicles were involved, so any information would be helpful to us."