Two vehicles were involved in the collision on the Lisnevenagh Road between Ballymena and Antrim.
It happened close to the Woodgreen Road junction this morning.
The emergency services rushed to the scene.
As a result, one person was taken to Antrim Area Hospital in a “serious condition”.
The road remains closed while the scene is examined by the PSNI’s Collision Investigation Branch.
Diversions are in place.
Police have issued an appeal for witnesses to come forward.
A PSNI spokesperson said: “Anyone who was on that stretch of road close to the Woodgreen Road junction between 9.30 am and 10 am and witnessed the collision is asked to contact police in Ballymena on the 101 non-emergency number.”