Traffic on the northbound A12 on the Essex and Suffolk border is being held due to an accident.
Suffolk roads police have halted traffic after reports of an overturned car.
Emergency services were called at around 9.40am to the incident.
Highways England tweeted that the incident is between junction 29-30, after Colchester and near Stratford St Mary
Junction 29 is the Ardleigh Crown Interchange linking with Ipswich Road into Colchester, while junction 30 serves Stratford St Mary.
Essex Police is also attending the incident.
A Suffolk Constabulary spokeswoman said details were still coming in, but initial reports suggested one lane may be re-opened around the scene.
The AA traffic control centre reports queuing traffic back to the first Dedham turn-off on the northbound carriageway.
We will bring you more details as we get them.
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