The M1 motorway is closed in both directions in West Yorkshire.
The northbound and southbound carriageways have been shut between Denny Dale and Ossett due to a "police incident".
Traffic has been building up and frustration has been growing among motorists. One onlooker said "dozens" of cars had been flying up the hard shoulder before U-turning in order to exit the motorway by going in the wrong direction along the slip road.
A traffic bulletin states: "M1 both ways closed due to police incident from J39 A636 Denby Dale Road (Wakefield / Durkar) to J40 A638 Wakefield Road (Ossett / Wakefield). The road has been closed since around 22:30 Friday night."
The motorway was expected to remain closed until at least 1am.
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