Motorists are facing 10 miles of congestion on the A12 after a two-vehicle crash.
Emergency services are currently at the scene of the crash in the southbound carriageway near Witham, where one lane is closed.
National Highways East has warned drivers of long delays while emergency services attend.
In a tweet, National Highways said: "On the A12 south between junction 21 and junction 20b near Witham, lane two of two is closed due to a collision.
"Emergency services are on scene and recovery are en route.
"Please allow extra time for your journey as delays of 45 minutes and 10 miles of congestion on the approach."
The number of vehicles involved and the extent of any injuries is not yet known.
Essex Police has been approached for a comment.
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