Multiple injured, one critical, after Transperth bus crashes into tree in Perth's north

Multiple passengers have been hurt after a Transperth bus crashed into a tree in Perth's north, with at least one person critically injured.

A St John WA spokesperson said at least five people had been taken to hospital after the accident, which happened just after 11am on Joondalup Drive in Wanneroo.

One of those passengers is in a critical condition at Joondalup Hospital, while another passenger was transported under priority one conditions to Royal Perth Hospital.

Three other passengers are being treated for non-life-threatening injuries.

Pictures show the front of the bus was significantly damaged after smashing into the tree.

Police remained at the scene on Thursday afternoon, with forensics officers marking up Joondalup Drive as they try to piece together what happened.

The crash forced the closure of Joondalup Drive between Burns Beach Road and Wanneroo Road, with motorists asked to avoid the area.

Separate crash shuts ED

The incident happened about an hour after a car crashed into St John of God hospital in Murdoch, in Perth's south, forcing the closure of its emergency department.

Police say the car was involved in collision with a male pedestrian before it smashed into the outside wall of a treatment ward just after 10am.

The pedestrian was taken to Royal Perth Hospital, while the male driver of the car is also receiving medical treatment.

No one inside the ward was injured.

Aphrodite Bouari was attending an appointment at the hospital when she said she heard a loud bang. She initially believed it was construction noise.

"So I didn't think of anything at all, and then when I came out, I'm like, oh my God," she said.

Police have urged anyone with relevant information or dashcam footage to contact Crime Stoppers.