A pregnant mother hit by a concrete block in a “senseless” attack in south Perth has died in hospital, along with her unborn child.

Diane Miller had been in a critical condition in intensive care at Royal Perth Hospital after suffering a heart attack when the block was thrown through the open window of her car at the Waterford shopping centre in Karawara on Tuesday night.

The 30-year-old Noongar woman was five months pregnant and also had an eight-month-old son.

She died overnight after her life support was turned off.

Her family had been told the baby would not survive if she died.

“Everyone’s destroyed,” her brother Malcolm Clifton told NITV News outside the hospital after her death.

“We just lost our world … the baby passed away too.”

Ms Miller’s brother with her toddler son Lloyde.

Western Australian Premier Mark McGowan said the attack had shocked Perth.

“Everyone is terribly sorry for her, her unborn child and her family,” he said.

“This is obviously an awful, awful, shocking, unexpected and unnecessary event.”

Waterford Plaza management also released a statement on Friday, expressing condolences to Ms Miller’s family and friends.

“[This] tragic death has shocked everyone who works and operates at the centre, as well as the broader community. Our thoughts and prayers are with all those that knew and loved her,” it said.

“Waterford Plaza is working closely with WA Police as they continue to investigate the circumstances surrounding this tragedy. We would like to thank the security officers, tenants and community who helped us
at our centre on Tuesday evening.”

The 17-year-old boy who allegedly threw the concrete block faced Perth Children’s Court on Wednesday charged with grievous bodily harm and breach of bail.

He was remanded in custody and is due to return to court on December 9.

But those charges could be upgraded after WA Police homicide detectives took over the investigation.

Police allege there was an argument involving a group of teenagers and Ms Miller’s partner, who was driving the car.

The parties are not believed to have been known to each other.

“This is, quite simply, senseless violence by a bunch of teenagers,” Inspector Brett Baddock said.

“From what we can gather, it’s unprovoked. I think they’ve gone out looking for trouble and they’ve found it.”

Passersby tried to resuscitate Ms Miller before an ambulance arrived.

-with AAP