Teen dies after hit by truck on Sydney M2

Police are investigating after a teenage pedestrian was hit and killed by a truck on the M2 in Sydney's west.

A teenage pedestrian is fighting for his life in hospital after being hit by a truck in Sydney. (AAP)

A teenage pedestrian has died after he was hit by a B-double truck on the M2 motorway in Sydney's west.

The 18-year-old was hit by the truck around 2.30am on Sunday on the M2 motorway at Seven Hills, police said.

He was treated at the scene before being taken to Westmead hospital in a critical condition where he died.

The driver has been treated for shock and is undergoing mandatory blood and urine testing.

It was the fifth fatal crash in NSW this weekend.