A Coroner has heard details of a horror crash in Mid Canterbury that killed a mother of seven and her two youngest children - a baby and toddler.

Chante Alissa Harmer, 30, died alongside her 19-month-old Te Awanuiarangi Shayelous-Jay Matenga Tapiata-Harmer and eight-month-old Wysdom Amara Francis Tony Jane Tapiata-Harmer after their car collided with another vehicle on April 2019 near Ashburton.

Harmer was driving her family members in a green Holden Astra, heading north along Hepburns Rd, which is controlled by give way signs.

Their vehicle collided with a Ford Ranger heading west along Mitcham Rd.

Harmer's car was torn in half in the crash.

A fourth person in Harmer's vehicle - a teenager - suffered critical injuries in the crash.

The driver of the Ford suffered minor injuries.

Both those injured have name suppression.

An inquest into the crash began this morning in the Ashburton District Court before Coroner Marcus Elliot.

The Herald is at the inquest and reporting on proceedings throughout the day.

Harmer was a much loved mother of seven.

She had recently moved to Ashburton from Hawkes Bay with her partner and children for a fresh start.

The crash was the second tragedy for the family, who lost a son in 2006 to cot death.

Coroner Elliot opened the hearing by acknowledging members of Harmer's family, who were in court to hear the graphic details of the crash.

The inquest will look into what caused Harmer's failure to give way, why she failed to notice a Give Way sign and whether the signage was enough to keep motorists safe.

At the time of the crash Harmer was on her way to her partner's workplace.

The court heard that she failed to give way and collided with the Ford.

Police said there was evidence Harmer was braking at the time of the crash but the give way sign - situated before the intersection - "blended into the background of the Canterbury landscape".

And the intersection itself had visibility issues for all drivers.

"Road signs and markings were not adequate to provide the safest environment possible for road users," the Coroner was told.

Later today evidence will be presented about three other crashes at the intersection.

The police - Give Way sign "easily missed"

Senior Constable John McIntyre - who has been part of the police Serious Crash Unit and is highly qualified and specialised in such investigations - was first to give evidence about the fatal incident.

He attended the crash soon after it happened.

He explained there was a Give Way sign at the intersection that was "clearly visible" from about 120m away.

There was also a painted triangle on the road.

However, he said the sign "could be easily missed as it blended with the background when observed from a distance".

"The driver did not stop at the Give Way sign," he said.

"The Ford collided with the right side of [Harmer's] car."

McIntyre said at some points of the intersection visibility was restricted by windbreak fencing.

Both Harmer and the other driver would have had an impeded view.

The court heard that there were no mechanical issues with either car - but Harmer's was not registered or warranted.

"She has become aware of the intersection and braked before impact, but not hard enough to lock in the wheels of her vehicle," McIntyre said.

Harmer had a restricted licence.

"It is not known if there were any internal distractions as she approached the intersection," the experienced police officer said.

The other driver saw Harmer come through the intersection and tried to swerve to avoid a crash.

She could not and collided with Harmer.

Photographs of the intersection were shown to Coroner Elliot including one of the Give Way sign taken from about 30m away.

It was barely visible.

"The further back you get, obviously the harder it was to see," said McIntyre.

The hedge would have reduced "any road users ability" to see what other vehicles were approaching the intersection.

McIntyre said once you were past the hedge, "you are fine" but before that visibility was problematic.

The inquest continues.