A seriously injured man has been flown to hospital after a crash which closed the A19.
The northbound carriageway near Crathorne has been closed all morning and is not expected to reopen until around 2pm .
One person had to be cut free by firefighers and was flown to Middlesbrough's James Cook Hospital by the Great North Air Ambulance.
Five others were treated at the scene.
Both carriageways were closed at one point. One lane southbound has now reopened but police are concerned rubbernecking motorists may cause another accident.
"Officers at the scene are concerned that a further collision will occur on the southbound carriageway due to drivers slowing down to look at the crash site," said a force statement.
"Police are asking motorists to keep moving at a safe speed and to concentrate on the road ahead of them.
"Thank you for your patience whilst the incident is being dealt with."
Cleveland Police are advising anyone travelling north to leave the A19 at the Stokesley junction.