A young woman is dead and her car ripped to pieces in one of the worst fatal collisions police said they've ever seen in Melbourne.

Authorities said the horrific crash occurred on the Nepean Highway in Cheltenham just before 5.30am yesterday.

The 25-year-old BMW driver, a woman from Dandenong, died at the scene.

Victoria Police said it was one of the worst crashes they've seen in Melbourne. (Nine)

Little was left of the BMW after the horrific crash. (Nine)

Her car, which police said was travelling well above 180km/h, skidded along the median strip before slamming into a traffic light.

The force of the crash ripped the car in half, spewing debris over six lanes of the road.

"It's an incredible scene and I've been in the police force for 30 years," Senior Sergeant Warren Francis-Pester told 9NEWS.

“I’ve never seen debris spread over six lanes of highway.

Police said the BMW was travelling at more than 180km./h. (Nine)

CCTV shows the moment the out-of-control car slammed into the pole. (Nine)

“The early indications here are that the speed was excessive.”

Police said drugs and alcohol were definite factors in the horror crash.

Snr Sgt Francis-Pester was on his way to work this morning when he saw the car flying past him.

Police spent much of the day cleaning up debris from the crash. (Nine)

Debris was left scattered over six lanes of highway. (Nine)

"I saw it coming through an activated speed camera, which alerted my attention," he said.

Earlier in the night, witnesses saw the the BMW driving erratically near Southland Shopping Centre.

At that point, she was travelling with a passenger, who feared for his life and got out of the car.

The Nepean Highway was closed in both directions near the intersection of Bay Road for several hours, but lanes have since reopened.

The crash brings the state death toll on Victorian roads so far this year to 156 - which is nearing equal to last year's number of 188, with another two months still to go.

A report will be prepared for the coroner.