The road is separated by a median strip in its centre, and it is unclear how the two cars collided head on.
One appears to have been on the wrong side of the road.
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There were unconfirmed,Discount Oakley Sunglasses, early suggestions that one of the cars may have taken a wrong turn from a nearby petrol station and driven into oncoming traffic.
The baby was inside a car with two other occupants - a man and a woman.
The baby was taken to the Canberra Hospital and was in a serious condition about 10pm last night.
The other car was driven by an ageing woman,Oakley Sunglasses Cheap, police say.
Paramedics say they took an adult woman to hospital,Oakley For Women, but it was unclear which car she was travelling in.
None of the adults were reported as having serious injuries.
The crash shut down southbound lanes on Melrose Drive for hours, while crash scene investigators combed through the scene.
The cars were still on the road just before 10pm.
The exact nature of the baby's injuries was unclear late on Sunday night.