A “critically injured” quad bike rider has been flown to hospital after a serious crash in Melaleuca on Saturday morning.

The RAC rescue helicopter was dispatched to the crash before landing in the vicinity of Tick Road around 10am.

A St John WA spokesperson said they were alerted to the incident after a man in his 20s was injured in the outer suburb — 45km north of Perth.

They said the rider was believed to be in a critical condition.

He was flown to Royal Perth Hospital, with the chopper arriving around 11.30am.

It comes after four people were killed in separate crashes since Thursday.

On Friday afternoon, a 52-year-old truck driver died the prime mover he was driving hit a tree in Red Gully, north of Gingin, about 2.05pm.

On Thursday around 8.30pm, a pair of drivers were killed in Wuraming when a grey Holden Commodore and grey Ford Falcon collided on Pinjarra Williams Road.

Both vehicles caught fire and the drivers died at the scene.

Also that evening about 6.50pm, a motorcycle rider died after a collision with a Toyota Landcruiser in Port Hedland.