Three people critically injured in spate of bad crashes over four hour span

Three people have been seriously injured in three separate car crashes on WA roads just four hours apart.

A 17-year-old girl was taken to Royal Perth Hospital with serious injuries after a car crashed into a tree on Saturday afternoon.

The accident occurred at around 12.55pm at the intersection of Thomas Road and Briggs Road in Byford. Three more people were injured.

A man in his 40s was taken to Armadale Hospital and a man and woman, both in their 30s, were taken to Fiona Stanley Hospital.

A separate crash involving a car and motorbike in Jarrahdale left a man in his 30s in a critical condition.

The crash happened just before 5pm on the corner of Jarrahdale Road and Blue Rock Road.

In the third crash, a man in his 20s was seriously injured when his truck overturned on Waratah Crescent in South Bunbury just after 5pm.