It is understood that an accident on the northbound A1 close to Wentbridge Viaduct, near Darrington, has closed the road.
Three miles of traffic has built up on the southbound carriageway, with a further six miles of congestion northbound.
Delays of up to an hour are expected.
In a tweet, Highways England said they were responding to a multi-vehicle accident which had blocked the carriageway.
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Traffic officers are on scene.
Two lanes have also been closed at junction 49 (Dishforth), in North Yorkshire, after a multi vehicle collision.