The A78 at Eglinton to Warrix was closed in both directions due to a serious road traffic collision, according to Amey SW Trunk Roads who originally reported the incident at 2am on Friday.
Emergency services were on the scene.
It is understood that is now only the southbound lane at Eglinton which remains closed due to the crash.
Local diversions are in place via Long Drive on the A71 and people can rejoin at the Warrix Interchange.
At Eglinton Interchange, people are being guided to exit onto the B7080, continue onto B736, then onto the A71 and then re-enter the A78.
Traffic Scotland has advised motorists to use the available signed diversion route.
People should expect a longer journey time than normal as a result of the incident.
Police Scotland has been contacted for comment.