Five critical after Sydney car crash

Five people, including a seven-year-old boy and his father, are fighting for their lives after a head-on crash in Sydney's northwest.

Police say a Subaru and a Lexus collided in Kellyville on Sunday afternoon leaving the 45-year-old driver of the Lexus trapped, along with his parents, aged 66 and 73.

The 53-year-old driver of the Subaru is also listed as critical, along with his seven-year-old son who has been taken to Westmead Children's Hospital with face, pelvic and chest injuries.

Police are appealing for witnesses to come forward.