Victorian police are pleading with drivers to slow down and wear their seatbelts after two young people died in a "completely avoidable" fatal crash on Sunday.

Key points: Witnesses told police the Mazda was driving erratically and speeding before the crash

Witnesses told police the Mazda was driving erratically and speeding before the crash A man in his teens remained in a critical condition in hospital

A man in his teens remained in a critical condition in hospital Police were investigating whether drugs and alcohol were involved

A young man and a woman in her teens died after the crash in Oakleigh East, south-east of Melbourne's CBD.

Police said a 19-year-old P-plater from Bayswater North was driving a green Mazda 3 when he hit a Nissan Skyline that was exiting a side street onto Ferntree Gully Road, between Clayton Road and Huntingdale Road, about 8:00pm.

Police said one of the cars caught fire after the collision.

The 21-year-old Hampton Park man behind the wheel of the Nissan died almost instantly.

The driver of the Mazda remained in a critical condition with head injuries.

He had three passengers and police said he was speeding and driving erratically before the crash occurred.

A woman, believed to be in her late teens, was rushed to hospital in a critical condition but died on Monday morning.

A teenage woman with arm injuries and a man in his 20s with pelvis injuries were in a stable condition.

Debris was seen strewn across the road after the crash. ( ABC News )

Kids driving 'lethal weapons': police

Detective Inspector Stuart McGregor, from the Major Collision Investigation Unit, said the crash was not an accident.

"This was completely avoidable, this is a deadly crash," he said.

"We should be doing everything we can so we don't have another person die on our roads for 2019 and yet we see behaviour like this."

Blood samples from both drivers were taken to determine is alcohol or drugs were involved.

Inspector McGregor said the driver of the Mazda was driving at high speed and "ducking and weaving" through lanes before the crash occurred.

"These are kids, children driving lethal weapons on our roads. We have to get the message through … we have two people who are dead and a person who is facing a long time in jail."

Charges have not yet been laid over the fatal collision.

The occupants of the cars are yet to be formally identified.

Local resident Nathan Beard arrived at the scene shortly after emergency services and said he was "devastated" to see the crash.

The former fireman said people needed to slow down on the road.

"Take extra care even if [you] have to stay under the speed limit," Mr Beard said.

Police said the driver of the Mazda and his female front seat passenger were assisting investigators with their enquiries.

Anyone who witnessed the crash or has dashcam footage is urged to contact Crime Stoppers.