It happened on the A64 between Bilbrough Top the junction with the A659.
The road is closed in both directions between those junctions.
Yorkshire Air Ambulance was in attendance.
The westbound carriageway is now open.
North Yorkshire Police said: "The A64 is currently closed eastbound due to a road traffic collision at Bilbrough.
"The A64 was closed in both directions for a short time to allow the air ambulance to land but the westbound carriageway is now open.
"Police, ambulance and fire crews are at the scene."
"Motorists are asked to avoid the area if possible".
The AA reports congestion, stationary traffic and serious delays.
Highways England expects traffic to return to normal from 4.15pm.