The A1 is currently closed in both directions between junctions 47 and 48, near Boroughbridge.
It follows a collision just after 4pm today (Monday 24 June 2013), on the northbound carriageway, involving two heavy goods vehicles.
As a result of the collision one of the lorries has spilled chemical into the carriageway. Police officers are working with colleagues from the North Yorkshire Fire and Rescue Service to establish the nature of the chemicals that have leaked.
The central reservation barrier has been taken down to allow the standing traffic on the north bound carriageway to turn around onto the south bound carriageway.
Fire Crews in Chemical Protection suits are attempting to stem the flow of the chemical to contain the spillage using soil and dry absorbent materials.
It is not know how long the road will remain closed and local diversions are being put in place.
See related news: A1 traffic and chemical incident now under control