The A12 has been closed in both directions near Colchester following a police-led incident, with motorists being warned of long delays.
National Highways confirmed the major route is shut between Junction 27 and Junction 29 in Essex.
The incident began shortly after 9.30am on Thursday, September 3, with Essex Police attending the scene and leading the response.
The nature of the police incident has not yet been disclosed.
Long delays expected around Colchester
National Highways has warned motorists to allow additional travelling time and consider changing or delaying their journeys.
Northbound traffic is being diverted off the A12 at Junction 27 and directed via the A133 through Colchester and A1232 Ipswich Road, before returning to the A12 at Junction 29.
Southbound motorists are being diverted at Junction 29 via the A1232 and A133 through Colchester, before returning to the southbound A12 at Junction 27.
Drivers are being urged to avoid the affected section if possible while emergency services remain at the scene.
There is currently no indication of when the road will reopen.
This is a developing incident and further updates will follow when more information is released.
