A passenger in the horrifying Wanneroo bus crash has died in hospital after sustaining critical injuries when the vehicle left the road and slammed into a tree.

The 61-year-old man died in hospital overnight, police revealed early Friday.

Emergency services rushed to Joondalup Drive in Wanneroo just after 11am on Thursday after the Transperth bus veered on to the wrong side of the road, mounted the kerb and slammed into a large tree.

Police say it is not yet known what caused the driver to lose control of the bus.

Multiple passengers were on board at the time, with eight occupants sustaining injuries.

A Transperth bus has crashed into a tree on Joondalup Drive, Wanneroo, Perth. Pictured: police at the scene on Thursday. A Transperth bus has crashed into a tree on Joondalup Drive, Wanneroo, Perth. Pictured: police at the scene on Thursday. Credit: Carwyn Monck/The West Australian

A 59-year-old female passenger was taken to Royal Perth Hospital for treatment of critical injuries.

Five other occupants were taken to Joondalup Health Campus and are receiving treatment for minor injuries.

The 56-year-old male bus driver was taken to Royal Perth Hospital for medical treatment.

Major Crash Investigation officers are examining what happened and inquiries into the incident are ongoing.

Anyone with footage can upload it directly to investigators.