Breaking: Child dead in alleged Sydney stabbing, two other children and woman critical

A child has died and two other children, and a woman, are in a critical condition after a stabbing in the Blue Mountains.

Police said all the children were under the age of five and the woman was in her 40s.

Just before 1pm today, emergency services received reports of three children and a woman in a vehicle with stab wounds on Waratah Road at Valley Heights, near Springwood.

"One of the children was located deceased in the vehicle," NSW Police said in a statement.

"NSW Ambulance paramedics treated the two children and the woman at the scene before they were conveyed to Westmead Hospital and Westmead Children's Hospital."

Several members of the public were rendering first aid as emergency services were being contacted.