Major Collision Investigation Unit detectives are investigating after a man sustained life-threatening injuries following a collision in Tooradin on Monday evening.
As of Tuesday morning the South Gippsland Highway remains closed to traffic in all directions at Dalmore Road following the collision.
It is believed a motorcycle and a BMW sedan were travelling along the South Gippsland Highway when they collided at about 6pm.
The 39-year-old male rider from Jam Jerrup sustained life-threatening injuries and was airlifted to hospital for treatment.
The driver of the sedan, a 35-year-old Newport man, was arrested at the scene and will be interviewed by police.
The exact circumstances surrounding the collision are yet to be determined and investigations remain ongoing.
Motorists heading south from Cranbourne should consider detouring via Berwick-Cranbourne Road to Clyde-Five Ways Road.
Then take Twyford Road onto Ballarto Road, through to Kooweerup Road to rejoin the South Gipplsland Highway. Northbound motorists should use the same route in reverse.
The closure of the South Gippsland Highway is under the control of emergency services. The Department of Transport said it is unknown how long the closure will be in place, however all lanes will open as soon as it is safe to do so.
Anyone who witnessed the collision or with footage is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at crimestoppersvic.com.au.