UPDATED

Three vehicles involved in a fiery truck crash on the Pacific Motorway at Somersby

Two people have died and at least three others have been injured in a horror crash on the Pacific Motorway on Tuesday afternoon.

Six NSW Ambulance crews responded Tuesday to the serious crash, involving a truck and two other vehicles in the northbound lanes of the M1, just north of the Mooney Mooney bridge.

NSW Police were called to the scene around 4.50pm where they found a truck had crashed into the back of two cars and caught fire.

Two people have died, however they are yet to be formally identified. NSW Ambulance said paramedics were treating four people at the scene.

A 44-year-old woman, who was driving one of two cars involved in the crash, has been taken by Ambulance to Gosford Hospital suffering chest pains.

An Ambulance spokesperson said that her vehicle was hit from behind before airbags deployed. She was able to get out of the vehicle and walk 50 metres from the crash site before being treated by paramedics.

A 75-year-old woman was also injured, suffering pain to her left arm, thigh and lower leg. She was able to escape her vehicle and was taken by Ambulance to Gosford Hospital for treatment.

The driver of the truck has been taken to Royal North Shore Hospital in a serious condition.

Ambulance were unable to provide further detail on the condition of the fourth patient.

All southbound lanes of the M1 Pacific Motorway have re-opened but two northbound lanes of the motorway remain closed.

Motorists have been advised to avoid the area as there are significant northbound delays, with traffic queued around seven kilometres from Mount White.

There is also very heavy traffic northbound traffic on the alternative route of the Pacific Highway.

Motorists who need to travel north are advised to allow plenty of extra travel time.

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