A string of crashes have unfolded in wet weather early this morning including a motorbike that collided with a car south of Perth.

A man in his 50s was on a Black Honda motorbike on North Lake Road in South Lake when he collided with a Grey Holden Commodore sedan near Elderberry Drive at about 5.45am.

The Holden driver was not hurt, but the motorcyclist was seriously injured and taken to Fiona Stanley Hospital.

A major emergency was triggered after a single car rollover in the southbound lanes of Kwinana Freeway at the Safety Bay Road exit in Baldivis.

Police say a red Mitsubishi ute lost control and rolled just after 5am with the injuries of those involved not yet known.

Emergency crews remain at the scene as Main Roads warn of heavy traffic travelling south.

A Toyota Hilux driver has also been taken to hospital after a crash in Darling Downs on South Western Highway near Thomas Road at about 6am.

St John Ambulance took a man in his 60s to Armadale Hospital where he is in a stable condition.

Main Roads has issued a warning of heavy traffic in both directions and advised drivers to proceed with caution.