A woman has died and a child is in a critical condition in hospital after a two-car crash on the A2 Bangor to Belfast road at Ballygilbert.
The Air Ambulance, three A&E crews, three rapid response paramedics and a doctor were sent to the scene of the crash, just after 15:45 GMT.
The A2 is closed in both directions at Ballyrobert.
Police said it was likely the road would remain closed for the rest of the evening.
The child has been taken to the Royal Belfast Hospital for Sick Children.