The pedestrian was struck by a lorry at the Moira Road roundabout on the Glenavy Road around 7.30 am this morning.
The PSNI have appealed for anyone who witnessed the incident to contact them.
The A26 Glenavy Road will be closed from 7 pm to 8 pm for a reconstruction and delays are expected.
Police are also investigating after two men were left seriously injured following a road crash in Co Antrim.
It happened on the Magheralane Road in Randalstown on Tuesday evening around 6 pm
The PSNI say the men were taken to Antrim Area Hospital for treatment.
The road remains closed this morning while the scene is examined by the PSNI’s Collision Investigation Branch.
Drivers are advised to avoid the area and seek an alternative route.