A pregnant mother hit by a concrete block in a “senseless” attack in suburban Perth is fighting for her life as homicide detectives take over an investigation.

Diane Miller remains in a critical condition in intensive care at Royal Perth Hospital, having suffered a heart attack when the brick was thrown through the open window of her car at a shopping centre in Karawara on Tuesday night.

The 30-year-old is five months pregnant and also has an eight-month-old son. Her family has been told the unborn baby will not survive if Ms Miller dies.

“We’re destroyed, shocked. She’s such a beautiful person and she would do anything for anybody,” brother Malcolm told Perth radio 6PR on Thursday.

“The family don’t know if she’s going to pull through. The doctor said that she’s got swelling on the brain and they said it’s not coming down.”

Teen charged with grievous bodily harm

A 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.

WA Police on Thursday said homicide squad detectives had taken on  the investigation and made a fresh appeal for public assistance.

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

Diane Miller is not expected to survive. Photo: Channel Nine screenshot

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.”

Passers-by attempted to resuscitate Ms Miller before an ambulance arrived. Her loved ones have said she suffered bleeding to her brain.

WA Premier Mark McGowan said it was a terrible situation for the family.

“It’s very, very sad for her and her unborn child. It’s one of those things that is just beyond description, that this could happen to someone,” he said.

Anyone who witnessed the incident or who has dash cam vision is asked to contact Crime Stoppers.

-AAP