Drivers are being advised to avoid the M23 at Crawley if possible while emergency services attend the scene of a three-vehicle collision at Junction 10.
At about 3.50pm on Wednesday (1 May) a lorry and two cars collided on the southbound carriageway, which was closed.
Emergency services attended the scene and diversions were put into place.
The northbound carriageway was also closed while an air ambulance attended to take a woman who had been driving one of the cars to Kings College Hospital in South London with injuries which were initially assessed as serious.
The northbound carriageway reopened at 5.35pm but the southbound carriageway remained closed.
Anyone who saw what happened is asked to contact Sussex Police online or by calling 101, quoting Operation Stonewall.
Newsdesk Guidance: No further information is available at this time - please bear with our busy operational colleagues in our Force Control Room busy dealing with this and all other incidents across Sussex.
Author: Tim Mahony