Another motorist travelling outbound on the Monash Freeway found the unconscious biker on the freeway between High Street and Warrigal Road at Malvern about 9.20pm.

Detectives from the Major Collision Investigation Unit suspect excessive speed was a factor in the crash.

It is believed the 47-year-old Mt Waverley man hit the centre concrete barrier on the freeway and skidded for 120 metres before slamming into a light pole.

Investigators are appealing for witnesses to come forward.

The motorcyclist's death brings the state's road toll to 49 - three more than at the same time last year.

Meanwhile, a motorist is lucky to be alive after powerlines fell over his car and trapped him following a separate smash in Mount Waverley on Monday.

The man was trapped in his car for 40 minutes.

Firefighters said a truck turning from Forster Road into Ricketts Road hit power lines and brought down a power pole shortly after 5am.

A man in his 70s driving behind the truck bore the brunt of incident, when the power lines fell over his car.

The MFB's Tony Birtwistle said the man did the right thing by staying in his car until emergency services arrived.

"He's perfectly OK. It was just a bit of a rude awakening this morning to have something like this happen to him," he told radio station 3AW.

Anyone with information is asked to contact Crime Stoppers on 1800 333 000.

- with Marissa Calligeros