A horrific three-vehicle collision that left two drivers trapped in the wreckage also left a toddler fighting for his life.
Emergency services were called to the Great Western Highway south of Blackheath in the Blue Mountains after receiving reports of a crash at around 7pm on Monday.
Initial police investigations suggest a semi-trailer collided head-on with a Subaru sedan before crashing into a Toyota Corolla.
A two-year-old boy who was travelling in the Subaru was rushed to Westmead Hospital in a critical condition after suffering serious head injuries.
NSW Police and Fire and Rescue crews freed the driver, a 27-year-old man, from the wreckage before taking him to the same hospital in a stable condition with leg and chest injuries.
The driver of the Toyota, a 29-year-old man, was also trapped in his car before being treated for internal injuries and taken to Nepean Hospital in a stable condition.
The 46-year-old truck driver suffered minor injuries and was taken to Katoomba Hospital for tests.
Traffic was re-routed around the crash site until Tuesday morning after the road was closed until about 2.45am when police established a crime scene.
A two-year-old boy is in a critical condition after suffering serious injuries in a three-vehicle crash on the Great Western Highway on Monday night (file image)
Specialist police from the Accident Investigation Unit were called to the scene, New South Wales Police said in a statement.
Anyone with information, including dashcam footage, is urged to contact police.