Police are appealing for information following yesterday's two-car crash on A2 Bangor to Belfast road at Ballygilbert which claimed the life of a woman and left a child in a critical condition.
A man was injured and taken to hospital for treatment.
The child has been taken to the Royal Belfast Hospital for Sick Children.
The air ambulance, three A&E crews, three rapid response paramedics and a doctor were sent to the scene of the crash, just after 3.45pm on Friday.
PSNI Inspector Jonny Francie is appealing for anyone on the road who may have seen something to call police on 101 quoting reference 847.
North Down DUP MLA Gordon Dunne said his thoughts and prayers are with the families.
"I would like to express my deepest sympathy to the family who were involved in a critical accident this afternoon on the A2 Dual Carriageway," he said.
"This is a very busy section of road and a sad event like this is a reminder of the dangers on our roads.
"I would also like to pay tribute to the emergency services who attended the scene today including the N Ireland Air Ambulance Service.
"I believe more investment is required by the Department of Infrastructure to improve safety on what is a very busy road with up to 45,000 vehicle movements each day.
"The maintenance of the road needs improvement to reduce risk to all users."
The A2, which had been closed to traffic following the accident, has now re-opened.