St Mary's crash: Sad update after boy, 5, and his mother were involved in horror accident between their car and a truck

A five-year-old boy has tragically died after the car he and his mother were travelling in slammed into a parked truck and trailer in the early hours of Friday.

Emergency services had to free the woman, 38, and her son from the wreckage following the collision on Christies St in the western Sydney suburb of St Marys at around 3.20am.

The pair were attended at the scene by ambulance crews before they were rushed to Westmead Hospital.

Both were in a critical condition before the boy passed away overnight. 

Harrowing photos of the the scene showed a white hatchback rammed into the back of the truck.

Debris was seen scattered across the road and the car's rear boot had been lifted up. 

It's believed the mother was driving and the child was a back-seat passenger. 

Police have set up a crime scene and launched an investigation into the cause of the crash.

Anyone with information about the incident is urged to contact Crime Stoppers on 1800 333 000.