Multiple people died in a crash involving a police vehicle and a car on the A66 in South Bank at around 3.39 am local time (0239GMT), Cleveland Police said in a statement, Anadolu Agency reported.
A spokesman for the force said: "Sadly, the collision has resulted in multiple fatalities. There are significant emergency vehicles on the scene, and the road will remain closed for some time."
It added that officers are working to identify the victims and contact their families.