The accident occurred on the Portaferry Road near Newtownards at around 8 am with police saying delays in the area are expected for some time.
A PSNI spokesperson said: “Serious traffic collision Portaferry Road.
“Traffic diverting via Finlay’s Road and Mountstewart Road.
“Delays expected for some time.
“All casualties have now been taken to hospital.
“Recovery has been tasked but it will possibly be another hour before reopening as Road has been damaged by fire and fluids.”
The Ambulance Service have said they received a 999 call at 7:55 am on Saturday following reports of a two vehicle road traffic collision on Portaferry Road, Co Down.
Two A&E crews and a doctor were tasked to the incident.
Following assessment and initial treatment at the scene, one patient was taken by ambulance to RVH.
A second patient was taken to Ulster Hospital Dundonald.