Witnesses have said it involves a police car and an SUV which has flipped onto its side - and that armed police are in attendance.
The road is closed between the A169 junction at Malton and B1248 Musley Bank.
The air ambulance has also landed at the scene.
-> Eight injured after 'big bang' stops plane from taking offNorth Yorkshire Police said in a tweet: We're at the scene of a collision on the A64 westbound near junction with B1257 near Malton. Expect traffic disruption in the area, please avoid if you can.”