Essex Police has issued an update following an incident on the southbound carriageway, which took place shortly before 7am.
The crash led to a road closure and long queues, however, one of the two lanes between Junction 17 Howe Green and Junction 16 Galleywood has now reopened.
A single vehicle was involved in the crash and damaged a barrier, which led to the temporary road closure.
A police spokesman said: “We were called to reports of a single vehicle collision on the southbound A12 between junctions 17 and 16 shortly before 7am on Wednesday 8 January.
“A barrier has been damaged during the incident.
“Both lanes were closed following the incident but one has since re-opened.
“If you have any information, CCTV, dash cam or other footage in relation to this incident, then please get in contact with us.
“Please quote incident 132 of 8 January.
“You can let us know by submitting a report on our website or by using our online Live Chat service which is available 24 hours-a-day, seven days-a-week.
“Visit www.essex.police.uk/digital101 to find out more about our online reporting services.
“If you would like to make an anonymous report you can contact independent charity @Crimestoppers, by visiting their website or by calling 0800 555 111.”
Heavy traffic remains in the area, and National Highways expects traffic conditions to return to normal between 9.45am and 10am.