At least one person is dead and six are in hospital after a petrol tanker collided with 10 other cars in a horror crash on a freeway in Melbourne's north west.

The truck is believed to have crushed one car with an unknown number of people trapped underneath, after it rolled on the Calder Freeway near Milleara Road, Keilor Park, about 8.40am, causing more cars to crash.

Emergency crews are on the scene, working to free the crushed car.

It’s believed the tanker was in the centre lane on the freeway when a car pulled in front of it, causing the truck to swerve and the driver to lose control of the vehicle, police have confirmed.

Five people have been taken to hospital in a stable condition, as well as a teenage boy as a precaution with no obvious injuries, Ambulance Victoria confirmed in a statement.

A woman in her 40s, whose car overturned, is being treated for neck, shoulder and arm injuries, at the Royal Melbourne Hospital.

A man who was driving the truck suffered leg injuries and is being treated at the Royal Melbourne Hospital.

Another woman in her 40s was taken to Sunshine Hospital with neck and hand injuries.

A woman aged in her 20s was also taken to Sunshine Hospital with neck and facial injuries.

Emergency crews are trying to get to the car trapped under the tanker. It is unknown how man people are inside. Picture: Facebook

A woman in her 60s was taken to Western Hospital, Footscray, with a wrist injury.

Two others, in addition to the teenager, were assessed at the scene.

The tanker was reportedly carrying 600 litres of diesel and 20,000 litres of unleaded petrol - up to 20,000 litres of which has spilled onto the freeway, the MFB has confirmed in a statement.

A 500 metre exclusion zone has been established while the MFB empties the tanker, closing the Calder Freeway outbound.

Motorists are being advised to avoid the area as roads are expected to be impacted most of the day.

One person is dead and at least six more injured after a petrol tanker rolled on a Melbourne freeway. Picture: Twitter/Dave_B86

CityLInk advised those travelling to the Tullamarine Airport to consider using the M80 Ring Road from the West Gate Freeway instead.

Some fuel has run into a nearby creek which will need to be pumped out.

A nearby school has reportedly relocated students to a different part of the campus.

The exact circumstances surrounding the collision are yet to be determined and detectives from the Major Collision Investigation Unit are investigating.

"Due to a significant amount of fuel still in the truck and on the road, police will need to wait for MFB crews to clear the scene before they can use equipment to cut into the crushed vehicle and further investigate," a Victoria Police spokesperson said in a statement.

Anyone who witnessed the collision is urged to contact Crime Stoppers on 1800 333 000.

Latest From 7News