Baby sisters in hospital after collision

Two baby sisters are in a serious but stable condition after the hatchback they were travelling in collided with a NSW Fire and Rescue truck driving in the same direction on the Pacific Highway in Sydney's north.

A 17-month-old girl sustained head injuries and a one-month-old girl was treated for head and abdominal injuries at the scene in Ku-ring-gai before being taken to Westmead Childrens' Hospital, police said.

Their mother, 28, sustained minor injuries in the Sunday afternoon collision, while their 29-year-old father was uninjured.

Police are investigating the incident.