The crash happened at around 12.30pm, and emergency services are on the scene.
The force said it expects the road to be closed for some time.
A short statement posted on its website said: "The A170 on the Thirsk side of Sutton Bank has been closed while emergency services attend a collision which occurred at around 12.30pm today (Sat 14 May 22.)
"Please avoid the area and find alternative routes, as officers expect the road to be closed for some time."
Anyone with information is asked to contact North Yorkshire Police on 101, quoting incident number NYP-14052022-0225.
The road reopened at around 4.30pm.