Graphic warning: Sickening moment Sydney street race goes bad, car veers off road into tree

A Sydney driver who failed to stop and assist a man who had rolled his car after a wild street race, and lay trapped with critical injuries, has had his conduct slammed by police.

Footage of two cars racing off at traffic lights in Sydney's west yesterday, along Cowpasture Rd, has been caught on dashcam.

The two hotted-up vehicles raced off at the green light but soon after one of the cars swerves off the road and flips on the median strip, hitting a tree.

His racing partner in a white car, however, continues to speed off up the road.

"This whole event was very dangerous. It’s lucky that the person who was injured in this collision was one of the drivers involved and no innocent member was injured," Acting Inspector Naomi Earle told 9NEWS.

"This is just stupidity - drivers driving stupid. There was no need for this collision to occur."

The 40-year-old driver who crashed, Foad Hellouc, suffered severe head injuries and remains in Liverpool Hospital, 50 minutes from Sydney CBD, in a critical but stable condition.

Fire fighters worked for more than an hour to extract Mr Hellouc from his crushed Mazda.