The air ambulance has been called to the scene of an accident involving a school bus and a car.
The crash happened on the Downpatrick road near Clough early on Friday morning.
Police said the male driver of the car and his male passenger have been taken to hospital.
The driver of the bus has also been taken to hospital.
The PSNI said 12 pupils were on board the bus, two of whom have been treated at the scene by paramedics.
A third pupil on the bus was taken from the scene to hospital for treatment.
Police said the injuries of the pupils on board the bus are not believed to be life threatening.
Local UUP councillor Alan Lewis said: "I thank the air ambulance team for their continued commitment and dedication to urgent response care within our community, an absolutely vital resource particularly at this time of deep uncertainty.
"My thoughts are with all those injured in this morning's incident, I hope and pray they make a full recovery, the entire community send their best wishes to all involved."
A PSNI spokesman said: "The Downpatrick road in Clough is closed in both directions following a road traffic collision involving a bus and a car. Local diversions are being put in place, however drivers are advised to seek alternative routes if possible."