An innocent motorist has been killed along with the driver of a speeding stolen car in a head-on smash north-west of Melbourne.

Highway police were alerted to the crash tragedy after the vehicle sped past them just minutes before the deadly impact.

Highway Patrol officers who had just intercepted an unrelated driver saw one of the cars speeding along a a regional road in Toolern Vale about 10am.

The speeding stolen vehicle continued on Diggers Rest-Coimadai Road before colliding head-on with a car travelling the other way.

The vehicles were flung metres from each other by the force of the smash.

Both drivers died at the scene.

A passenger travelling in the speeding car was taken to the Royal Melbourne Hospital in a serious but stable condition.

Locals said there were often people travelling along the stretch of road well beyond the speed limit.

“It’s a collision scene that spreads well over 100 metres,” Detective Inspector Craig McEvey said.

“It’s carnage, to be honest, it’s horrific.”

The Major Collision Investigation Unit was expected to remain on scene for some time.

The drivers were yet to be formally identified.