UPDATE: One young man is dead and another person is critically injured after a crash in Wattle Grove last night.
A four-wheel-drive vehicle collided with two people riding a motorcycle on Hale Road, near the intersection of Welshpool Road, about 7.35pm.
An 18-year-old man on the motorbike died at the scene.
The other person on the motorbike was seriously injured and remains in a critical condition in Royal Perth Hospital.
The driver of the 4WD is not believed to have been seriously injured.
Police said this morning that the red Honda motorcycle was heading east on Welshpool Road East when it entered the intersection at Hale Road.
"At the same time, a white utility also entered the intersection [and] the two vehicles collided," police spokesman Samuel Dinnison said.
Major Crash investigators are calling for information from the public.
Anyone with information about the crash - or who saw either of the vehicles before the crash - is asked to call Crime Stoppers on 1800 333 000.